Genesis 35:22-26

35:22 While Israel was living in that land, Reuben had sexual relations with ¹  Bilhah, his father’s concubine, and Israel heard about it.

Jacob had twelve sons:

35:23 The sons of Leah were Reuben, Jacob’s firstborn, as well as Simeon, Levi, Judah, Issachar, and Zebulun.

35:24 The sons of Rachel were Joseph and Benjamin.

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.

¹ tn Heb “and Reuben went and lay with.” The expression “lay with” is a euphemism for having sexual intercourse.