From a 1977 interview in The Paris Review:

Vonnegut: I just discovered a prayer for writers. I'd heard of prayers for sailors and kings and soldiers and so on -- but never a prayer for writers. Could I put that in here?

Interviewer: Certainly.

Vonnegut: It was written by Samuel Johnson on April 3, 1753, the day on which he signed a contract which required him to write the first complete dictionary of the English language. He was praying for himself. Perhaps April third should be celebrated as "Writers' Day." Anyway, this is the prayer: "O God, who hast hitherto supported me, enable me to proceed in this labor, and in the whole task of my present state; that when I shall render up, at the last day, an account of the talent committed to me, I may receive pardon, for the sake of Jesus Chris. Amen.

Interviewer: That seems to be a wish to carry his talent as far and as fast as he can.

Vonnegut: Yes. He was a notorious hack.
 

From "The Art of Fiction, No. 64," Issue 69, Spring 1977.
 

"Kurt Vonnegut, 1922 - 2007," Chicago Tribune, 4/12/07
"Kurt Vonnegut," Guardian Unlimited, 4/12/07
"Kurt Vonnegut, Counterculture's Novelist, Dies," New York Times, 4/12/07