Genesis 35:22 New Revised Standard Version (NRSV)
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.
1 Chronicles 5:1 New Revised Standard Version (NRSV)
Descendants of Reuben
5 The sons of Reuben the firstborn of Israel. (He was the firstborn, but because he defiled his father’s bed his birthright was given to the sons of Joseph son of Israel, so that he is not enrolled in the genealogy according to the birthright;