Genesis 35:22-24 Revised Standard Version (RSV)
22 While Israel dwelt 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 first-born), Simeon, Levi, Judah, Is′sachar, and Zeb′ulun. 24 The sons of Rachel: Joseph and Benjamin.