Abraham Circumcised by Shem at Midday on Yom Kippur

"In the selfsame day." Rabban Gamliel says: He sent and called Shem son of Noah, and he circumcised Abraham and Ishmael his son, as it is said, "In the selfsame day, etc." What is "in the selfsame day"? In the strength of the sun, at midday. And not only that, but on the tenth of the month, on this Day of Atonement, as it is said, "and you shall do no manner of work in the selfsame day" (Leviticus 23:28); and concerning Abraham it is written "in the selfsame day." From here, that he did not delay to perform the circumcision: on the very day that the Holy One, blessed be He, spoke with him, on that same day he circumcised them and uncovered them. And from where do you say that the Holy One, blessed be He, told him to circumcise and to uncover? Another interpretation: "In the selfsame day" — in the full openness of the day, and not in secret. And every year the Holy One, blessed be He, sees the blood of Abraham's covenant and atones for the sins of Israel, as it is said, "for on this day He shall make atonement" (Leviticus 16:30).