Hebrews 11:18

of which first-born it was said: In Isaac shall your posterity be called:

Romans 9:7-8

Nor, because they are the posterity of Abraham, are they all children: but in Isaac shall your posterity 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 posterity of Abraham, are they all children: but in Isaac shall your posterity be called.
Hebrews 11:18
of which first-born it was said: In Isaac shall your posterity be called: