Buddha's Refutes the Notion that Tathagatagarbha is the Upanishadic Atman, or that the Buddhist Nirvana is the same as Upanishadic Moksha, from the Lankavatara Sutra

Then Mahamati said to the Blessed One: In the Scriptures mention is made of the Womb of Tathagatahood and it is taught that that which is born of it is by nature bright and pure, originally unspotted and endowed with the thirty-two marks of excellence. As it is described it is a precious gem but wrapped in a dirty garment soiled by greed, anger, folly and false-imagination. We are taught that this Buddha-nature immanent in everyone is eternal, unchanging, auspicious. It is not this which is born of the Womb of Tathagatahood the same as the soul-substance that is taught by the philosophers? The Divine Atman as taught by them is also claimed to be eternal, inscrutable, unchanging, imperishable. It there, or is there not a difference?
���The Blessed One replied: No, Mahamati, my Womb of Tathagatahood is not the same as the Divine Atman as taught by the philosophers. What i teach is Tathagatahod in the sense of Dharmakaya, Ultimate Oneness, Nirvana, emptiness, unbornness, unqualifiedness, devoid of will-effort. The reason why I teach the doctrine of Tathagatahood is to cause the ignorant and simple-minded to lay aside their fears as they listen to the teaching of egolessness and come to understand the state of non-discrimination and imagelessness. The religious teaching of the Tathagatas are just like a potter making various vessels by his own skill of hand with the aid of rob, water and thread, out of the one mass of clay, so the Tathagatas by their command of skillful means issuing from Noble Wisdom, by various terms, expressions, and symbols, preach the twofold egolessness in order to remove the last trace of discrimination that is preventing disciples from attaining a self-realisation of Noble Wisdom. The doctrine of the Tathagata-womb is disclosed in order to awaken philosphers from their clinging to the notion of a Divine Atman as a transcendental personality, so that their minds that have become attached to the imaginary notion of a "soul" as being something self-existing, may be quickly awakened to a state of perfect enlightement. All such notions as causation, succesion, atoms, primary elements, that make up personality, personal soul, Supreme Spirit, Sovereing God, Creator, are all figments of the imagination and manifestations of mind. No, Mahamati, the Tathagata’s doctrine of the Womb of Tathagatahood is not the same as the philosopher’s Atman.

later

[Buddha] They ("philosophers") imagine that Nirvana consists (of) ... the absorption of the finite-soul in the supreme Atman; or who see all things as a manifestation of the vital-force of some Supreme Sprit to which all return; (...)
���... clinging to these foolish notions, there is no awakening, and they consider Nirvana to consist in the fact that there is no awakening.

Chapter 9, Madhyamakakarika
���1. Certain people say: Prior to seeing hearing, and other [sensory faculties] together with sensation and other [mental phenomena] Is that to which they belong.
���2. [They reason:] How will there be seeing, etc. of someone (i.e. as the subject seeing) who does not exist? Therefore, there exists a definite (vyavasthita) entity before that [seeing, etc.].
���3. But that definite entity is previous to sight, hearing, etc., and sensation, etc -- How can that [entity] be known?
���4. And if that [entity] is determined without sight [and other sensory faculties], Then, undoubtedly, those [sensory faculties] will exist without that [entity].
���5. Someone becomes manifest by something (i.e. like vision); something is manifest by someone. How would someone exist without something? How would something exist without someone?
���6. [The opponent admits:] Someone does not exist previous to (purva) sight and all the other [faculties] together. [Rather,] he is manifested by any one of [them:] sight, etc., at any one time.
���7. [Nagarjuna answers:] But if nothing exists previous to sight and all the other [faculties] together, How could that [being] exist individually before sight, etc.?
���8. [Further,] if that [being] were the "seer," that [being] were the "hearer," that [being] were the one who senses, Then one [being] would exist previous to each. Therefore, this [hypothesis] is not logically justified.
���9. On the other hand, if the "seer" were someone else, or the "hearer" were someone else, or the one who senses were someone else, Then there would be a "hearers when there was already a "seer," and that would mean a multiplicity of "selves" (atma).
���11. When he to whom seeing, hearing, etc., and feeling, etc. belong does not exist, Then certainly they do not exist.
���12. For him who does not exist previous to, at the same time, or after seeing, etc. The conception "He exists," "He does not exist," is dissipated.

Shunyatasaptati
���56. Consciousness occurs in dependence on the internal and external sense-fields. Therefore consciousness is empty, like mirages and illusions.
���57. Since consciousness arises in dependence on a discernible object, the discernible does not exist [in itself]. Since [the conscious subject] does not exist without the discernible and consciousness, the conscious subject does not exist [by itself].

Bodhicittavivarana
���4. When the self imagined by the tirthikas is analyzed logically, it obtains no place within the [five] skandhas.
���5. If it were [identical with] the skandhas [the self] would not be permanent, but the self has no such nature. And between things permanent and impermanent a container-content relationship is not [possible].
���6. When there is no so-called self how can the so-called creator be permanent? [Only] if there were a subject might one begin investigating its attributes in the world.
���7. Since a permanent [creator] cannot create things, whether gradually or all at once, there are no permanent things, whether external or internal.
���8. Why [would] an efficacious [creator] be dependent? He would of course produce things all at once. A [creator] who depends on something else is neither eternal nor efficacious.
���9. If [he] were an entity he [would] not be permanent, for things are perpetually instantaneous (since [you] do not deny that impermanent things have a creator).
���36. Considering that without a body there is no consciousness, you must also state what kind of specific knowledge of itself this [consciousness] possesses!
���39. The knowable is known by a knower. Without the know-able no knowing [is possible]. So why not accept that subject and object do not exist [as such]?
���40. Mind is but a name. It is nothing apart from [its] name. Consciousness must be regarded as but a name. The name too has no own-being.
���53. Whoever regards consciousness as momentary cannot accept it as permanent. If mind is impermanent, how does this contradict sunyata?

Madhyamakavatara

VI.79
Those who are outside the path of Master Nagarjuna have no means of peace. They depart from the truths of convention and thatness, and, because they depart from them, cannot attain liberation. VI.121-125
A self that is an experiencer, a permanent thing, a non-creator, and without qualities or activity is fabricated by the Tirthikas (heretics, non-Buddhists). Through finer and finer distinctions, different traditions of the Tirthikas have evolved. [But] Since such a self is not born, it does not exist, just like a child of a barren woman; and since it is not even the basis of grasping at I, it cannot be asserted even conventionally. All the characteristics attributed to it by the Tirthikas in this treatise and that treatise are damaged by the reason of its not being born, with which they are familiar; therefore none of these characteristics exists. Thus there is no self that is other than the aggregates (in Advaita, koshas) because it is not apprehended separate from the aggregates. It cannot even be asserted as the basis of worldly I-grasping minds, because though they do not cognize it, they have a view of self. Even those who have spent many aeons as animals do not see this unborn permanent; and yet they too are seen to grasp at I. Therefore there is no self that is other than the aggregates.

VI.146-149
Some assert a substantially existent person who is indescribable in terms of sameness, otherness, permanence, impermanence, and so forth. They say it is an object of knowledge of the six consciousnesses, and assert that it is the basis of grasping at I. Since you do not assert mind to be indescribable with respect to form, you should not assert existent things to be indescribable. If self exists as a thing, existent things, like mind, are not indescribable. According to you a pot, which is an entity not existing as a thing, is indescribable with respect to form and so forth. Therefore, you should not assert a self indescribable with respect to its aggregates existing by itself. You do not assert that consciousness is other than its own nature, but you do assert it to be a thing that is other than form and so forth. Since these two aspects are seen in things, the self does not exist because it lacks the characteristics of things.

IX. Bodhicaryavatara
���60. If the awareness of sound were I, then sound would always be apprehended. But without an object of awareness, what does it cognize on account of which it is called awareness?
���61. If that which is not cognizant were awareness, a piece of wood would be awareness. Therefore, it is certain there is no awareness in the absence of its object.
���62. Why does that which cognizes form not hear it as well?
[Samkhya:] Because of the absence of sound, there is no awareness of it.
���63. [Madhyamika:] How can something that is of the nature of the apprehension of sound be the apprehension of form? One person may be considered as a father and as a son, but not in terms of ultimate reality,
���64. Since sattva, rajas, and tamas are neither a father nor a son. Moreover, its nature is not seen as related to the apprehension of sound.
���65. If it is the same thing taking another guise, like an actor, he too is not permanent. If he has different natures, then this unity of his is unprecedented.
���66. If another guise is not the true one, then describe its natural appearance. If it were the nature of awareness, then it would follow that all people would be identical.
���67. That which has volition and that which has no volition would be identical, because their existence would be the same. If difference were false, then what would be the basis for similarity?
��� 68. That which is not conscious is not "I," because it lacks consciousness, like a cloth and the like. If it were conscious because it has consciousness, then it would follow that when it stops being conscious of anything, it would vanish.
���69. If the Self is not subject to change, what is the use of its consciousness? Thus, this implies that space, which lacks consciousness and activity, has a Self. ��� 70. [Objection:] Without the Self, the relationship between an action and its result is not possible, for if the agent of an action has perished, who will have the result?
���71. [Madhyamika:] When both of us have agreed that an action and its result have different bases and that the Self has no influence in this matter, then there is no point in arguing about this.
���72. One who has the cause cannot possibly be seen as being endowed with the result. It is pointed out that the existence of the agent and the experiencer of the consequences depends on the unity of their continuum of consciousness.
���73. The past or future mind is not "I," since it does not exist. If the present mind were "I," then when it had vanished, the "I" would not exist any more.
���74. Just as the trunk of a plantain tree is nothing when cut into pieces, in the same way, the "I" is non-existent when sought analytically.
���75. [Qualm:] If no sentient being exists, for whom is there compassion?
[Madhyamika:] For one who is imagined through delusion, which is accepted for the sake of the task.
���76. [Qualm:] If there is no sentient being, whose is the task?
[Madhyamika:] True. The effort, too, is due to delusion. Nevertheless, in order to alleviate suffering, delusion with regard to one's task is not averted.
���77. However, grasping onto the "I," which is a cause of suffering, increases because of the delusion with regard to the Self. If this is the unavoidable result of that, meditation on identitylessness is the best.