Hebrews 11:18

Of whom it was said, That in Isaac shall thy seed be called:

Cross-reference

Genesis 17:19 is the original promise that Abraham's offspring would come through Isaac — quoted in Hebrews 11:18.

Genesis 21:12 is the direct source of the quote in Hebrews 11:18 — 'Through Isaac shall your offspring be named.'

Romans 9:7 also quotes Genesis 21:12 — Paul uses the same promise to argue that not all descendants are true children.