Contradiction with Genesis 10:25
Genesis 10:25 attributes two sons to Eber, contradicting the lineage brevity implied in Genesis 25:12.
Genesis 10:25: And unto Eber were born two sons: the name of one [was] Peleg; for in his days was the earth divided; and his brother's name [was] Joktan. [Peleg: that is Division]
Contradiction with Genesis 17:20
Ishmael is promised to be fruitful and a great nation, contrasting with the brief mention of his lineage in Genesis 25:12.
Genesis 17:20: And as for Ishmael, I have heard thee: Behold, I have blessed him, and will make him fruitful, and will multiply him exceedingly; twelve princes shall he beget, and I will make him a great nation.
Contradiction with Genesis 16:12
Describes Ishmael's character as a "wild man," which contrasts with the neutral description of his genealogy in Genesis 25:12.
Genesis 16:12: And he will be a wild man; his hand [will be] against every man, and every man's hand against him; and he shall dwell in the presence of all his brethren.
Contradiction with Genesis 17:18
Abraham's plea for Ishmael to live before God suggests a significant role for Ishmael, which is downplayed in Genesis 25:12.
Genesis 17:18: And Abraham said unto God, O that Ishmael might live before thee!