“One who is eight days old shall be circumcised among you, every male throughout your generations, born in the house, or purchased with silver from any foreigner, who is not of your descendants” (Genesis 17:12). “One who is eight days old shall be circumcised among you” – it is taught: One who purchases the fetus of an idolater’s maidservant, Rabbi Yoḥanan said: He should be circumcised on the eighth day.41As opposed to one who purchases an already-living baby as a slave; he requires circumcision on the day he is bought, even if it is before he is eight days old (see Shabbat 135a).
And Rabbi Ḥama bar Yosei [also] taught: He should be circumcised on the eighth day. Shmuel taught the same, as Shmuel said: “For a son and for a daughter” (Leviticus 12:6) – in all cases.42That passage mentions the circumcision of a baby on his eighth day (Leviticus 12:3).