Genesis 35:22
20 Jacob set up a marker over her grave; it is the Marker of Rachel’s Grave to this day. 21 Then Israel traveled on and pitched his tent beyond the Tower of the Flock.43 22 While Israel was living in that land, Reuben went to bed with Bilhah, his father’s concubine, and Israel heard about it. Jacob had twelve sons: 23 The sons of Leah were Reuben, Jacob’s firstborn, as well as Simeon, Levi, Judah, Issachar, and Zebulun. 24 The sons of Rachel were Joseph and Benjamin.
Jubilees 33:2
1 Jacob went and lived to the south of the Tower of Eder Ephrathah. He went to his father Isaac — he and his wife Leah — on the first of the tenth month. 2 When Reuben saw Bilhah, Rachel's maid — his father's concubine — bathing in water in a private place, he loved her. 3 At night he hid. He entered Bilhah's house at night and found her lying alone in her bed and sleeping in her tent. 4 After he had lain with her, she awakened and saw that Reuben was lying with her in the bed. She uncovered the edge of her clothing, took hold of him, shouted out, and realized that it was Reuben. 5 She was ashamed because of him. Once she had released her grip on him, he ran away. 6 She grieved terribly about this matter and told no one at all.
Notes and References
"... Reuben is most popularly known as the brother who sought to protect Joseph from being killed. However, the Testament dwells entirely on a brief episode recounted in Genesis 35:22 ... Here in his “testament,” Reuben returns to this episode as well. The story is significantly expanded. Reuben sees Bilhah bathing naked, which plants the idea of fornication with her into his mind. When his father, Jacob, is away visiting Isaac, Reuben enters Bilhah’s tent, finds her naked and uncovered (she had apparently been drinking), and has sex with her without awakening her. As soon as the act is done, an angel informs Jacob about what had happened. He mourns over Reuben and has no further relations with Bilhah. Reuben is afflicted with a disease in his genitalia for seven months and nearly dies, but Jacob prays on his behalf, and God spares him. Convicted of his guilt, Reuben does penance by abstaining from meat, alcohol, and pleasant foods for seven years, remaining conscience-stricken throughout his life. This retelling of the story closely resembles the version found in Jubilees 33:1–8. There, too, Reuben sees Bilhah bathing, enters her tent secretly, and lays with her while she sleeps. In Jubilees, however, Bilhah awakens during the act, cries out aloud, and tells Jacob upon his return about what transpired ..."
DeSilva, David A. The Jewish Teachers of Jesus, James, and Jude: What Earliest Christianity Learned from the Apocrypha and Pseudepigrapha (p. 177) Oxford University Press, 2012