Genesis 35:22-24 World English Bible (WEB)
22 While Israel lived in that land, Reuben went and lay with Bilhah, his father’s concubine, and Israel heard of it.
Now the sons of Jacob were twelve. 23 The sons of Leah: Reuben (Jacob’s firstborn), Simeon, Levi, Judah, Issachar, and Zebulun. 24 The sons of Rachel: Joseph and Benjamin.