Abram's wife Sarai had never had any children by him. But she had a female servant from Egypt named Hagar.
References for Genesis 16:1
So she said to Abram, "The LORD has kept me from having children. Go and make love to my servant. Maybe I can have a family through her." Abram agreed to what Sarai had said.
After he had been living in Canaan for ten years, his wife Sarai gave him her servant Hagar to be his wife.
He made love to Hagar. And she became pregnant. When Hagar knew she was pregnant, she began to look down on the woman who owned her.
Then Sarai said to Abram, "It's your fault that I'm suffering like this. I put my servant in your arms. Now that she knows she's pregnant, she looks down on me. May the LORD judge between you and me. May he decide which of us is right."
"Your servant belongs to you," Abram said. "Do with her what you think is best." Then Sarai treated Hagar badly. So Hagar ran away from her.