Genesis 21:8-21

"But God told Abraham, 'Do not be upset over the boy and your servant. Do whatever Sarah tells you, for Isaac is the son through whom your descendants will be counted. 13But I will also make a nation of the descendants of Hagar’s son because he is your son, too.'" v12-13
As a dad, it must have been hard to send away your son. Abraham had to do just this and trust that the Lord would provide for their needs.

Ever wounder what happened to Ishmael and who his descendants were? Ismael became ruler of a large tribe or nation. The Ishmaelites were nomads living in the wilderness of Sinai and Paran, south of Israel. One of Ishmael's daughters married Esau, Ismael's nephew. The Bible pictures the Ishmaelites as hostile to Israel and the God.

Taken from the NLT Life Application Study Bible