Genesis 21:13

And also of the son of the bondwoman will I make a nation, because he is thy seed.

Cross-reference

Genesis 21:18 reaffirms the same promise about Ishmael becoming a great nation.

Genesis 17:20 details the blessing on Ishmael, directly supporting this promise.

Genesis 25:12–18 Prophetic fulfillment

Genesis 25:12-18 records Ishmael becoming twelve princes and a nation — the direct fulfillment of God's promise about Abraham's seed here.

In Genesis 16:10, God promised to multiply Hagar's descendants, echoing the promise here.