Whom did Sarah tell Abraham to send away?

Answer: Hagar and Ishmael

Seeing Hagar's son mocking Isaac, Sarah told Abraham to expel the slave woman and her son.

“But Sarah saw that the son whom Hagar the Egyptian had borne to Abraham was mocking her son, and she said to Abraham, “Expel the slave woman and her son, for the slave woman’s son will never share in the inheritance with my son Isaac!””— Genesis 21:9-10 (BSB)