While Israel stayed in that place, Reuben went and slept with Bilhah his father's secondary wife, and Israel heard about it. Jacob had twelve sons.
References for Genesis 35:22
The sons of Leah were Reuben, Jacob's oldest son, and Simeon, Levi, Judah, Issachar, and Zebulun.
The sons of Rachel were Joseph and Benjamin.
The sons of Bilhah, Rachel's servant, were Dan and Naphtali.
The sons of Zilpah, Leah's servant, were Gad and Asher. These were Jacob's sons born to him in Paddan-aram.