Abram casting out Hagar and her son Ishmael (with Sarai in the background)
Painting by Giovanni Francesco Barbieri, 1657

Abram and Sarai Try To Play God: The Birth Of Ishmael (GENESIS 16:9-16)

It all goes back to God's promise to make Abram the father of many nations and give him the land of Canaan as an eternal inheritance for him and his heirs (GENESIS 12. The problem came when Sarai persuaded Abram to get a son by sleeping with her maid Hagar. Hagar conceived and gave birth to a son,

Sarai's inability to conceive a son of her own resulted in bitterness towards Hagar and led to Hagar's expulsion. In her distress Hagar cried out to God who appeared to her in the form of an angel and announced:

"You shall name him ISHMAEL (meaning 'God hears') for the Lord has heard of your misery.He will be a wild donkey of a man; his hand will be against everyone and everyone’s hand against him, and he will live in hostility toward all his brothers."

God Promises A Son To Abram & Sarai: The Birth Of ISAAC (GENESIS 17:15-22)

A while later God appears to Abram - now renamed Abraham  -  and tells him to call Sarai "Sarah" from now on and announces that she is going to have a son. When Abraham laughs at the apparent impossibility of such an idea, since he will be one hundred and Sarah ninety if this happens, God says:

"“Yes, but your wife Sarah will bear you a son, and you will call him ISAAC (meaning "he laughs"). He will establish my covenant with him as an everlasting covenant for his descendants after him. And as for ISHMAEL, I have heard you: I will surely bless him; I will make him fruitful and will greatly increase his numbers. He will be the father of twelve rulers, and I will make him into a great nation. But I will establish my covenant with Isaac, whom Sarah will bear to you by this time next year.”

The Hostility Between Ishmael vs Isaac: Precursor To Arab vs Israeli Hostility

ISHMAEL is traditionally regarded as the ancestor of the ARABS, who have traditionally been enemies of the descendants of Isaac's son Jacob, later renamed ISRAEL.