According to Pirkei D’Rebbi Eliezer 29, Shem Ben Noach performed Avraham’s Bris. My question concerns the other opinion in Beresheit Rabba 49b that Avraham performed it himself.
According to this opinion, how was Avraham’s Brit valid? I don’t have a source, but I recall a non-Jew cannot become a ger by giving himself a Brit milah.
I do know Shulchan Aruch Yorah Deah 264:1 stipulates:
אבל עובד כוכבים אפי' הוא מהול לא ימול כלל
Although the above quote concerns if one were already circumcised, one can possibly infer their circumcisions are not valid.
I understand one might cite the Gemara in Avodah Zara (10b I think) that Ketiah Bar Shalom’s self-performed Bris is a proof that a a non-Jew should be able to do it. However, my inquiry concerns Avraham’s act with respect to Shulchan Aruch. It goes without saying this proceeds from the assumption that Avraham acted in accordance with Torah law prior to its endowment to Bnei Yisrael.