Genesis 35:22-26

And it came to pass, when Israel dwelt in that land, that Reuben went and lay with Bilhah his father's concubine: and Israel heard it. Now the sons of Jacob were twelve: the sons of Leah; Reuben, Jacob's firstborn, and Simeon, and Levi, and Judah, and Issachar, and Zebulun: the sons of Rachel; Joseph, and Benjamin: and the sons of Bilhah, Rachel's handmaid; Dan, and Naphtali: and the sons of Zilpah, Leah's handmaid; Gad, and Asher: these are the sons of Jacob, which were born to him in Padan-aram.