While Israel was living in that region, Reuben went in and slept with his father's concubine Bilhah, and Israel heard of it. Jacob had twelve sons: (NIV)
When Israel dwelt there, Reuben [his eldest son] went and lay with Bilhah his father's concubine; and Israel heard about it. Now Jacob's sons were twelve. (AMP)
And it came to pass, when Israel dwelt in that land, that Reuben went and lay with Bilhah his father's concubine: and Israel heard it. Now the sons of Jacob were twelve: (KJV)