Genesis 30:3-8

30:3 She replied, “Here is my servant Bilhah! Have sexual relations with her so that she can bear children for me and I can have a family through her.”

30:4 So Rachel gave him her servant Bilhah as a wife, and Jacob had marital relations with her. 30:5 Bilhah became pregnant and gave Jacob a son. 30:6 Then Rachel said, “God has vindicated me. He has responded to my prayer and given me a son.” That is why she named him Dan.

30:7 Bilhah, Rachel’s servant, became pregnant again and gave Jacob another son. 30:8 Then Rachel said, “I have fought a desperate struggle with my sister, but I have won.” So she named him Naphtali.