Ari M. asked:
It's not clear to me what the source (Pasuk) is for the Isur of Shichvas Zera? Is it only derived from Er v'Onan? If so, then why is it not Asur for Nochrim (or is it)?
Thank you!
The Kollel replies:
Tosfos in Sanhedrin (59b) writes that the Isur is based on the Mitzvas Aseh of Peru u'Revu. Therefore, since this Mitzvah does not apply to Nochrim, Nochrim have no Isur of Shichvas Zera.
However, see Minchas Chinuch (#1), who cites in the name of the Ramban that Benei Noach are indeed Metzuveh in the Mitzvah of Peru u'Revu, and in the Isur of S"Z as well, and it was for transgressing that Isur that they were destroyed in the Mabul.
D. Zupnik