Page 45 and 46 of Hazel E. Barnes translation of Sartre's Being and Nothingness

  One can apply to Hegel what Le Senne said of the philosophy of Hamelin:  "Each of
the lower terms depends on the higher term, as the abstract on the concrete which is
necessary for it to realize itself." The true concrete for Hegel is the Existent with
its essence; it is Totality produced by the synthetic integration of all the abstract
moments which are surpassed in it by requiring their complement. In this sense being
will be the most abstract of abstractions and the poorest, if we consider it in itself
- that is, by separating it from its surpassing toward essence. In fact "Being is
related to Essence as the immediate to the mediate. Things in general 'are,' but their
being consists in manifesting their essence. Being passes into Essence. One can express
this by saying, 'Being presupposes Essence.' Although Essence appears in relation to
Being as mediated, Essence is nevertheless the true origin. Being returns to its
ground; Being is surpassed in Essence."
  Thus Being cut from Essence which is its ground becomes "mere empty immediacy." This
is how the Phenomenology of Mind defines it by presenting pure Being "from the point
of view of the truth" as the immediate. If the beginning of logic is to be the
immediate, we shall then find beginning in Being, which is "the indetermination which
precedes all determination, the undetermined as the absolute point of departure.
  But Being thus undetermined immediately "passes into" its opposite. "This pure
Being," writes Hegel in Logic (of the Encyclopedia), is "pure abstraction and
consequently absolute negation, which taken in its immediate moment is also non-being."
Is Nothingness not in fact simple identity with itself, complete emptiness, absense
of determinations and of content? Or rather it is true to say that they are different;
but "as here the difference is not yet a determined difference - for being and 
non-being constitute the immediate moment such as it is in them - this difference
cannot be named; it is only a pure opinion." This means concretely that "there is
nothing in heaven or on earth which does not contain in itself being and nothingness."