1And the Lord visited Sarah as he had said, and the Lord did unto Sarah as he had spoken.

2 For Sarah conceived, and bare Abraham a son in his old age, at the set time of which God had spoken to him.

3 And Abraham called the name of his son that was born unto him, whom Sarah bare to him, Isaac.

4 And Abraham circumcised his son Isaac being eight days old, as God had commanded him.

5 And Abraham was an hundred years old, when his son Isaac was born unto him.

6 And Sarah said, God hath made me to laugh, so that all that hear will laugh with me.

7 And she said, Who would have said unto Abraham, that Sarah should have given children suck? for I have born him a son in his old age.

8 And the child grew, and was weaned: and Abraham made a great feast the same day that Isaac was weaned.

9 And Sarah saw the son of Hagar the Egyptian, which she had born unto Abraham, mocking.

10 Wherefore she said unto Abraham, Cast out this bondwoman and her son: for the son of this bondwoman shall not be heir with my son, even with Isaac.

11 And the thing was very grievous in Abraham's sight because of his son.

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.

13 And also of the son of the bondwoman will I make a nation, because he is thy seed.

Source: Bible, excerpts copied from the International Bible Society
https://www.biblica.com/bible/kjv/genesis/21/

SUMMARY OF THE REMAINING OF THE CHAPTER:

The boy and his mother were sent to the desert. When the water ran out, the mother left the boy and walked away from him. God heard the boy crying and spoke to his mother. He told her not to worry, because the boy will have many children. God opened the vision of the mother, and she saw a well.

Abram makes an oath for the king to be true to him. But he complained of a well that was taken by the king's people, and the king declares that he did not know the matter. Abraham gives sheep to the king in testimony that it was Abraham who dug the well. And so they made agreement.