Genesis 16:1-3

Living Bible

16 But Sarai and Abram had no children. So Sarai took her maid, an Egyptian girl named Hagar, ^2-3 and gave her to Abram to be his second wife.

“Since the Lord has given me no children,” Sarai said, “you may sleep with my servant girl, and her children shall be mine.”

And Abram agreed. (This took place ten years after Abram had first arrived in the land of Canaan.)