It's based on Bereishi 4:1 "And the man knew"
Rashi here notes that Cain and Abe (and their three sisters) were born before the sin:
(This is what it says in the notes to my English edition of Rashi: "Rashi bases this statement on the syntactical rule that when, in a naarative, a series of imperfects with Vau Conversive is followed by a perfect, it has a pluperfect sense, the action it describes having taken place previous to the event mentioned immediately before it")
It's expounded in Bereishis Rabbah 22, in the gemara in Sanhedrin 38b, which elaborates on Bereishis 4:1, and commentaries on the gemara, in the midrash Pirkei de R' Eliezer, and the Zohar in Bereishis 36b
Archive powered by MHonArc 2.6.24.