Hebrews 11:18

unto whom it had been said, "That by Isaac shall there be a seed bearing thy name:"

Romans 9:7-8

nor, because they are the seed of Abraham, are they all children: but, in Isaac shall thy seed be called.

Treasury of Scripture Knowledge

Summary

And God said unto Abraham, Let it not be grievous in thy sight because of the lad, and because of thy bondwoman; in all that Sarah hath said unto thee, hearken unto her voice; for in Isaac shall thy seed be called.

Bible References

In isaac

Romans 9:7
nor, because they are the seed of Abraham, are they all children: but, in Isaac shall thy seed be called.
Hebrews 11:18
unto whom it had been said, "That by Isaac shall there be a seed bearing thy name:"