Genesis 35:21-23 Revised Standard Version (RSV)
21 Israel journeyed on, and pitched his tent beyond the tower of Eder.
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.