So the child grew and was weaned, and Abraham held a great feast on the day Isaac was weaned. 9But Sarah saw that the son whom Hagar the Egyptian had borne to Abraham was mocking her son,
Genesis 21:8-9
But just as at that time he who was born according to the flesh persecuted him who was born according to the Spirit, so also it is now.
Galatians 4:29
This occurred 30 years after Abraham left Haran and 400 years before Israel had departed both the Land of Canaan and then Egypt through the Exodus with Moses. Beginning the time from which would fulfil:
Then YHVH said to Abram, “Know for certain that your offspring will be sojourners in a land that is not theirs and will be servants there, and they will be afflicted for 400 years.”
Genesis 15:13
Sarah Turns against Hagar
10Therefore she said to Abraham, “Drive out this maid and her son, for the son of this maid shall not be an heir with my son Isaac.” 11The matter distressed Abraham greatly because of his son. 12But God said to Abraham, “Do not be distressed because of the lad and your maid; whatever Sarah tells you, listen to her, for through Isaac your descendants shall be named. 13“And of the son of the maid I will make a nation also, because he is your descendant.” 14So Abraham rose early in the morning and took bread and a skin of water and gave them to Hagar, putting them on her shoulder, and gave her the boy, and sent her away. And she departed and wandered about in the wilderness of Beersheba.
15When the water in the skin was used up, she left the boy under one of the bushes. 16Then she went and sat down opposite him, about a bowshot away, for she said, “Do not let me see the boy die.” And she sat opposite him, and lifted up her voice and wept. 17God heard the lad crying; and the angel of God called to Hagar from heaven and said to her, “What is the matter with you, Hagar? Do not fear, for God has heard the voice of the lad where he is. 18“Arise, lift up the lad, and hold him by the hand, for I will make a great nation of him.” 19Then God opened her eyes and she saw a well of water; and she went and filled the skin with water and gave the lad a drink.
20God was with the lad, and he grew; and he lived in the wilderness and became an archer. 21He lived in the wilderness of Paran, and his mother took a wife for him from the land of Egypt.
Covenant with Abimelech
22Now it came about at that time that Abimelech and Phicol, the commander of his army, spoke to Abraham, saying, “God is with you in all that you do; 23now therefore, swear to me here by God that you will not deal falsely with me or with my offspring or with my posterity, but according to the kindness that I have shown to you, you shall show to me and to the land in which you have sojourned.” 24Abraham said, “I swear it.” 25But Abraham complained to Abimelech because of the well of water which the servants of Abimelech had seized. 26And Abimelech said, “I do not know who has done this thing; you did not tell me, nor did I hear of it until today.”
27Abraham took sheep and oxen and gave them to Abimelech, and the two of them made a covenant. 28Then Abraham set seven ewe lambs of the flock by themselves. 29Abimelech said to Abraham, “What do these seven ewe lambs mean, which you have set by themselves?” 30He said, “You shall take these seven ewe lambs from my hand so that it may be a witness to me, that I dug this well.” 31Therefore he called that place Beersheba, because there the two of them took an oath.32So they made a covenant at Beersheba; and Abimelech and Phicol, the commander of his army, arose and returned to the land of the Philistines. 33Abraham planted a tamarisk tree at Beersheba, and there he called on the name of YHVH, the Everlasting God. 34And Abraham sojourned in the land of the Philistines for many days.