Contradiction with Genesis 21:12
In Genesis 17:15 Abram's wife is to be called Sarah, emphasizing the promise through her, while Genesis 21:12 promises the lineage through Isaac, her son, as opposed to other descendants.
Genesis 21:12: 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.