Genesis 17:21 is the original promise about Isaac at the set time, which Romans 9:9 quotes directly.

Genesis 18:10 repeats the promise of a son to Sarah at the appointed time, quoted here.

Genesis 18:14 affirms nothing is too hard for the LORD and repeats the promise, aligning with this verse's citation.

Genesis 21:2 records the fulfillment: Sarah conceives at the exact time God promised, showing the promise kept.

Hebrews 11:11 highlights Sarah's faith in receiving power to conceive, reflecting the same promise event.

In Hebrews 11:17, this same promised son Isaac becomes the test of Abraham's faith.

Genesis 17:16 explicitly promises Sarah will have a son, the same promise Paul quotes.

Galatians 4:28 applies the same promise of Isaac to believers as children of promise.