But My covenant I will establish with Isaac, whom Sarah shall bear to you at this set time next year."
Genesis 17:21
Surrounding context
17:20 And as for Ishmael, I have heard you. Behold, I have blessed him, and will make him fruitful, and will multiply him exceedingly. He shall beget twelve princes, and I will make him a great nation.
17:21 But My covenant I will establish with Isaac, whom Sarah shall bear to you at this set time next year."
17:22 Then He finished talking with him, and God went up from Abraham.