help about Foucault

Is there anybody who can help me?

I remember Foucault states something like
"discourse is a response to a crisis at a historically specific
mement." My problem is I can't locate the source of the idea in any of
Foucault's books.  I do not remember the exact statement either.

Help me to find where I can find the passage.

Boo Eung Koh in Korea.