Genesis 16:2-4

So Sarai said to Abram, “The LORD has prevented me from having children. Go and sleep with my servant. Perhaps I can have children through her.” And Abram agreed with Sarai’s proposal. So Sarai, Abram’s wife, took Hagar the Egyptian servant and gave her to Abram as a wife. (This happened ten years after Abram had settled in the land of Canaan.) So Abram had sexual relations with Hagar, and she became pregnant. But when Hagar knew she was pregnant, she began to treat her mistress, Sarai, with contempt.