EXTRA · Parashas Vayeishev · Passuk 37:29 · not a Torah Temimah citation on this passuk
When Reuben returned to the pit and saw that Joseph was not in the pit, he rent his clothes.
Classical source (EXTRA side-ring): Bereshis Rabbah 84:19.
Sefaria — Bereshis Rabbah 84:19
English: “And Reuven returned to the pit” — where had he been? R’ Eliezer said: in his sackcloth and his fasting.
Derash on the verse (Bereshis Rabbah) — not a formal named middah of the 13. Absence is explained by private teshuvah.
Reuven’s delay was occupied with repentance; he meant to rescue Yosef, but arrived too late.