Genesis 35:22

New English Translation

²²While Israel was living in that land, Reuben went to bed with^[a] Bilhah, his father’s concubine, and Israel heard about it.

Jacob had twelve sons:

Genesis 35:22 tn Heb “lay down with.” The verb שָׁכַב (shakhav) “to lie down” can imply going to bed to sleep or be a euphemism for sexual relations.sn Reuben’s act of having sexual relations with Bilhah probably had other purposes than merely satisfying his sexual desire. By having sex with Bilhah, Reuben (Leah’s oldest son) would have prevented Bilhah from succeeding Rachel as the favorite wife, and by sleeping with his father’s concubine he would also be attempting to take over leadership of the clan—something Absalom foolishly attempted later on in Israel’s history (2 Sam 16:21-22).

New English Translation (NET)