Genesis 16:1-4 NIV
Now Sarai, Abram’s wife, had borne him no children. But she had an Egyptian slave named Hagar; so she said to Abram, “The LORD has kept me from having children. Go, sleep with my slave; perhaps I can build a family through her.”
Abram agreed to what Sarai said. So after Abram had been living in Canaan ten years, Sarai his wife took her Egyptian slave Hagar and gave her to her husband to be his wife. He slept with Hagar, and she conceived.
When she knew she was pregnant, she began to despise her mistress.
NIV: New International Version