Genesis 35:22

35:22 While Israel was living in that land, Reuben had sexual relations with Bilhah, his father’s concubine, and Israel heard about it.

Jacob had twelve sons:

Genesis 35:25-26

35:25 The sons of Bilhah, Rachel’s servant, were Dan and Naphtali.

35:26 The sons of Zilpah, Leah’s servant, were Gad and Asher.

These were the sons of Jacob who were born to him in Paddan Aram.