Genesis 21:7-11

And she said, “Who would have said to Abraham that Sarah would nurse children? Yet I have given birth to a son in his old age.”

And the child grew and was weaned, and Abraham held a great feast on the day that Isaac was weaned. Sarah Turns against Hagar

Now Sarah saw the son of Hagar the Egyptian, whom she had borne to Abraham, mocking Isaac.

Therefore she said to Abraham, “Drive out this slave woman and her son, for the son of this slave woman shall not be an heir with my son Isaac!”

The matter distressed Abraham greatly because of his son Ishmael.