Genesis 35:22

בשכן ישראל בארץ ההוא WHEN ISRAEL DWELT IN THAT LAND — before he came to Isaac at Hebron, all these troubles happened to him. וישכב AND HE LAY — Because he had disturbed his couch Scripture accounts it to him as though he had actually sinned in this manner. But why did he disturb his couch? When Rachel died Jacob removed to Bilhah’s tent and Reuben came and protested against the slight thus inflicted on his mother (Leah). He said: “If my mother’s sister was her rival, is that any reason why the handmaid of my mother’s sister should become a rival to her!” On this account he disturbed the couch (Shabbat 55b). ויהיו בני יעקב שנים עשר NOW THE SONS OF JACOB WERE TWELVE — Scripture begins again where it left off the previous narrative (i.e. the birth of Benjamin): when Benjamin was born the destined number of his sons was complete and it was proper that they should then be enumerated; and therefore it enumerates them. Our Rabbis explained that these words are intended to tell us that Jacob’s twelve sons were all equal — they were all equally righteous, for Reuben had committed no actual sin (Shabbat 55b).

וַיְהִ֗י בִּשְׁכֹּ֤ן יִשְׂרָאֵל֙ בָּאָ֣רֶץ הַהִ֔וא וַיֵּ֣לֶךְ רְאוּבֵ֗֔ן וַיִּשְׁכַּ֕ב֙ אֶת־בִּלְהָ֖ה֙ פִּילֶ֣גֶשׁ אָבִ֑֔יו וַיִּשְׁמַ֖ע יִשְׂרָאֵ֑͏ֽל׃ {פ}וַיִּֽהְי֥וּ בְנֵֽי־יַעֲקֹ֖ב שְׁנֵ֥ים עָשָֽׂר׃

And it came to pass, when Yisra᾽el dwelt in that land, that Re᾽uven went and lay with Bilha his father’s concubine: and Yisra᾽el heard of it. Now the sons of Ya῾aqov were twelve: