First Prayer

I was surprised to find that the word "pray" doesn't appear until Genesis 20.

Abimelech was tricked into taking Abraham's wife, Sarah, into his harem. God appears to Abimelech in a dream and threatens his whole household with death if he doesn't return Sarah to Abraham.

Abimelech agrees to these terms but states his innocence. God agrees, but tells Abimelech that Abraham will pray for his forgiveness.

This places much more of the process of forgiveness on an intermediary than I'd expect.