Abram's wife Sarai had not borne him any children. But she had an Egyptian slave woman named Hagar,
and so she said to Abram, "The Lord has kept me from having children. Why don't you sleep with my slave? Perhaps she can have a child for me." Abram agreed with what Sarai said.
So she gave Hagar to him to be his concubine. (This happened after Abram had lived in Canaan for ten years.)
Abram had intercourse with Hagar, and she became pregnant. When she found out that she was pregnant, she became proud and despised Sarai.
Then Sarai said to Abram, "It's your fault that Hagar despises me. I myself gave her to you, and ever since she found out that she was pregnant, she has despised me. May the Lord judge which of us is right, you or me!"
References for Genesis 16:5
Abram answered, "Very well, she is your slave and under your control; do whatever you want with her." Then Sarai treated Hagar so cruelly that she ran away.