Genesis 16:1-2

1Now Sarai, Abram’s wife, had not borne him any children, and she had an Egyptian maid whose name was Hagar.

2So Sarai said to Abram, “See here, the Lord has prevented me from bearing children. I am asking you to go in to [the bed of] my maid [so that she may bear you a child]; perhaps I will obtain children by her.” And Abram listened to Sarai and did as she said.