Genesis 30:3-6
3 Then she said, “Here is Bilhah, my maidservant. Sleep with her so that she can bear children for me and that through her I too can build a family.”
4 So she gave him her servant Bilhah as a wife. Jacob slept with her,
5 and she became pregnant and bore him a son.
6 Then Rachel said, “God has vindicated me; he has listened to my plea and given me a son.” Because of this she named him Dan.