Where does the Bible say salvation is attainable through faith alone?

James 2:18 Yea, a man may say, Thou hast faith, and I have works: shew me thy faith without thy works, and I will shew thee my faith by my works.

A Jew arguing for faith+works ("I have works"), says against James' "law of liberty" ("Thou hast faith"):

"You contradict reality, as faith cannot exist without works. That fact is manifest even in what you just taught about salvation by a "law of liberty", where you say 'while we are saved by faith alone, (law of liberty) saving faith is never alone,it always radiates good works'."

Its a logical argument: "You cannot prove your faith exists without works, if you can show me such faith exists without works, then I will believe you. In contrast, I can show you my faith+works by the works.

James' rebuts the "vain man" (i.e., "empty man", who in reality does not have works to his credit), his argument for Mosaic law fails him for two sound reasons:

1)Since Orthodox faith (monotheism figuratively stands here for the entire Mosaic law) without works does not save, the demons believe yet are lost;
2)Since demonic faith in the truth about God is so intense they tremble, its evidence faith without works can exist.

James 2:19 Thou believest that there is one God; thou doest well: the devils also believe, and tremble. 20 But wilt thou know, O vain man, that faith without works is dead?

Then James resumes explaining how real saving faith is always accompanied with works, as it causes them. God's purpose for faith is realized when good works appear in our sphere, then God's plan is completed...faith is perfected, it accomplished what God created it to do:

James 2:21 Was not Abraham our father justified by works, when he had offered Isaac his son upon the altar? 22 Seest thou how faith wrought with his works, and by works was faith made perfect? 23 And the scripture was fulfilled which saith, Abraham believed God, and it was imputed unto him for righteousness: and he was called the Friend of God. 24 Ye see then how that by works a man is justified, and not by faith only. 25 Likewise also was not Rahab the harlot justified by works, when she had received the messengers, and had sent them out another way? 26 For as the body without the spirit is dead, so faith without works is dead also.

A man "by works is Justified (dikaioo)", i.e., we know them by their fruits, works and faith together "declare the man righteous (to us)", that it is saving faith that exists in him. Conversely, a dead body proves it does not have animating spirit, therefore the vain man's lack of actual good works proves he does not have saving faith. (cp Matt 7:16-20)

From God's perspective, we are saved by grace alone....from our perspective, we believe and then are saved....but God is the one who facilitated our belief, having predestined it before the founding of the world, before we did any works:

Romans 11:5-6 5 Even so then at this present time also there is a remnant according to the election of grace. 6 And if by grace, then is it no more of works: otherwise grace is no more grace. But if it be of works, then is it no more grace: otherwise work is no more work.

Ephesians 1:3 Blessed be the God and Father of our Lord Jesus Christ, who hath blessed us with all spiritual blessings in heavenly places in Christ: 4 According as he hath chosen us in him before the foundation of the world, that we should be holy and without blame before him in love: 5 Having predestinated us unto the adoption of children by Jesus Christ to himself, according to the good pleasure of his will, 6 To the praise of the glory of his grace, wherein he hath made us accepted in the beloved. 7 In whom we have redemption through his blood, the forgiveness of sins, according to the riches of his grace;

Ephesians 2:4-10 4 But God, who is rich in mercy, for his great love wherewith he loved us, 5 Even when we were dead in sins, hath quickened us together with Christ, (by grace ye are saved;) 6 And hath raised us up together, and made us sit together in heavenly places in Christ Jesus: 7 That in the ages to come he might shew the exceeding riches of his grace in his kindness toward us through Christ Jesus. 8 For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: 9 Not of works, lest any man should boast. 10 For we are his workmanship, created in Christ Jesus unto good works, which God hath before ordained that we should walk in them.

The saving Faith God gifts us with is never alone, its the beginning of God's workmanship, we are created in Christ Jesus unto good works. In other words, this saving faith causes us to appear in the realm of Christ, for the purpose of doing the good works God ordained us to do.

So Catholics misunderstand salvation by grace through faith....it is not saying evil men can be saved by a phony profession of faith

Matthew 7:20 Wherefore by their fruits ye shall know them. 21 Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven. 22 Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works? 23 And then will I profess unto them, I never knew you: depart from me, ye that work iniquity. 24 Therefore whosoever heareth these sayings of mine, and doeth them, I will liken him unto a wise man, which built his house upon a rock: 25 And the rain descended, and the floods came, and the winds blew, and beat upon that house; and it fell not: for it was founded upon a rock. 26 And every one that heareth these sayings of mine, and doeth them not, shall be likened unto a foolish man, which built his house upon the sand: 27 And the rain descended, and the floods came, and the winds blew, and beat upon that house; and it fell: and great was the fall of it.

__________________
The times of this ignorance God winked at; but now commandeth all men every where to repent:

Behold, I stand at the door, and knock: if any man hear my voice, and open the door, I will come in to him, and will sup with him, and he with me.-kjv