Genesis 21:2

Sarah became pregnant and bore a son to Abraham in his old age, at the very time God had promised him.

(New International Version)

So Sarah conceived and bore a son to Abraham in his old age, at the appointed time of which God had spoken to him.

(New American Standard Bible)

For Sarah conceived, and bare Abraham a son in his old age, at the set time of which God had spoken to him.

(King James Version)