Genesis 30:3-9

3And she said, Behold, my maid Bilhah, go in unto her; that she may bear upon my knees, and I also may obtain children by her. 4And she gave him Bilhah her handmaid to wife: and Jacob went in unto her. 5And Bilhah conceived, and bare Jacob a son. 6And Rachel said, God hath judged me, and hath also heard my voice, and hath given me a son: therefore called she his name Dan. 7And Bilhah Rachel’s handmaid conceived again, and bare Jacob a second son. 8And Rachel said, With mighty wrestlings have I wrestled with my sister, and have prevailed: and she called his name Naphtali.

9When Leah saw that she had left off bearing, she took Zilpah her handmaid, and gave her to Jacob to wife.