Indeed, it was Adorno, but the quote is a bit thornier than people
recollect (after all, it's Adorno).  There are actually 2 quotes:  one,
the original statement, then a later (modified) retraction:
 
In 1949, in "Cultural Critique and Society" Adorno writes:
"To write poetry after Auschwitz is barbaric.  And this corrodes even the
knowledge of why it has become impossible to write poetry today."
 
Then, in *Negative Dialectics* he writes:
"Perennial suffering has as much right to expression as a tortured man has
to scream; hence it may have been wrong to say that after Auschwitz you
could no longer write poems."