Sarai, Abram's wife, had not been able to have children. Since she had an Egyptian servant named Hagar,
References for Genesis 16:1
Sarai said to Abram, "The LORD has kept me from giving birth, so go to my servant. Maybe she will provide me with children." Abram did just as Sarai said.
After Abram had lived ten years in the land of Canaan, Abram's wife Sarai took her Egyptian servant Hagar and gave her to her husband Abram as his wife.
He slept with Hagar, and she became pregnant. But when she realized that she was pregnant, she no longer respected her mistress.
Sarai said to Abram, "This harassment is your fault. I allowed you to embrace my servant, but when she realized she was pregnant, I lost her respect. Let the LORD decide who is right, you or me."
Abram said to Sarai, "Since she's your servant, do whatever you wish to her." So Sarai treated her harshly, and she ran away from Sarai.