Genesis 30:3-8

3Then she said, “Here is Bilhah, my servant. Sleep with her so that she can bear children for me and I too can build a family through her.” 4So she gave him her servant Bilhah as a wife. Jacob slept with her, 5and she became pregnant and bore him a son. 6Then Rachel said, “God has vindicated me; he has listened to my plea and given me a son.” Because of this she named him Dan. 7Rachel’s servant Bilhah conceived again and bore Jacob a second son. 8Then Rachel said, “I have had a great struggle with my sister, and I have won.” So she named him Naphtali.