Hebrews 11:18

of whom it was said, In Isaac shall your posterity be called,

Romans 9:7-8

neither, because they are a 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
neither, because they are a posterity of Abraham, are they all children; but in Isaac shall your posterity be called;
Hebrews 11:18
of whom it was said, In Isaac shall your posterity be called,