Genesis 16:3-4

After Abram had lived in the land of Canaan ten years, Abram’s wife Sarai took Hagar the Egyptian [maid], and gave her to her husband Abram to be his [secondary] wife. He went in to [the bed of] Hagar, and she conceived; and when she realized that she had conceived, she looked with contempt on her mistress [regarding Sarai as insignificant because of her infertility].