Halakha Keluaran 24:8: Mishneh Torah, Circumcision & Mishneh Torah, Forbidden Intercourse

A proselyte must, before he can enter the communion of Israel be circumcised. If, while still a gentile, he had already been circumcised, it is requisite to draw a drop of blood from the membrum, on the day when he is received, as a sign of the covenant. Similarly, if a male infant is born with the prepuce absent, it is requisite to draw a drop of blood from the membrum when the infant is eight days old. An androgyne that has both male and female organs is to be circumcised on the eighth day. So too a male infant delivered by the Caesarean operation, or one born with two foreskins is to be circumcised on the eighth day.

And God does not bring on them an abundance of punishment so that they will not be lost. Rather, all of the nations of the world are finished off, and they will remain. And they go on at length about this matter, in order to endear it to them. If he retracts and does not want to accept, he can go on his way. And if he accepts, they do not delay him. Rather they circumcise him immediately. And if he was already circumcised they spill some covenantal blood, and they delay him until he fully heals, and then they immerse him.