Genesis 17:15

Overview - Genesis 17
1	God renews the covenant with Abram, and changes his name to Abraham, in token of a greater blessing.
9	Circumcision is instituted.
15	Sarai's name is changed to Sarah, and she is blessed.
17	Isaac is promised, and the time of his birth fixed.
23	Abraham and Ishmael are circumcised.

Genesis 17:15  (King James Version)
And God said unto Abraham, As for Sarai thy wife, thou shalt not call her name Sarai, but Sarah shall her name be.