Shulchan Arukh, Yoreh De'ah 265/שולחן ערוך·יורה דעה רס״ה

1Order of the blessings of the Bris and Laws of Bris on fast day.The circumciser blesses “who sanctified us with his commandments and commanded us regarding circumcision.” The father blesses between the cutting of the foreskin and peeling back: “who sanctified us with his commandments and commanded us to bring him into the covenant of Abraham, our father.” Rema: If the father of the boy is not at the Bris, there are those who say that another man makes this blessing because the court is obligated to circumcise him (Rambam) and our practice is that the one who holds the boy makes this blessing (Tur in the name of the Raavad and Hagahot Maimoniyot in the name of the Smak). So too if the father is at the Bris, but does not know how to make the blessing (Rabbeinu Yerucham). The father and the mohel need to stand when they bless, but the one holding the boy customarily sits when he blesses. There are those who say that all people at the Bris must stand because it says that “all the nation stood in covenant.” This is our custom except for the one holding the boy who sits down. And if others are standing there, they say “just as you brought him into the covenant, so too should you bring him in to Torah, to the wedding canopy, and to good deeds.” The father or the mohel, or one of the people there blesses on a cup: “who creates the fruit of the vine.” And some have the custom to take a myrtle in their hands, to bless on it and to smell it. He says “Blessed are You, Adonoy our God, King of the Universe, who sanctified his dear one from the womb etc.” Our custom is when we reach “BeDamayich Chayii” to put wine on his finger and in the mouth of the baby. (And when the mohel makes the blessing, he should wipe his hands and mouth first so that he does it in cleanliness.) (Abudarham)

2If the father of the boy is the mohel, he blesses “to circumcise a son” according to the Rambam. (But there are those who disagree, (Tur in the name of the Baal Haitur) and our custom is not to differentiate. However, if he blessed “limol” or “lehachnieso” alone, he has fulfilled his obligation) (Hagahot Maimoniyot)

6When it is possible, the circumcision should be done among 10 individuals, and when it is not possible, it can be done among less than 10.

7When the father himself is circumcising his son, he makes the blessing Shehachayenu, and if the one who is doing the circumcising is someone else, there are those who say that the blessing Shehachayenu is not said, and according to the Rambam, the father always makes the blessing שהחיינו for every circumcision, and this is how we practice in all of the community of the land of Israel, and in Syria, and in its environs, and in the Egyptian community. Rema: And in these places, the custom is not to bless Shehachayenu, even when the father himself is circumcising his son, unless he is circumcising his firstborn son who is obligated in being redeemed, then he makes the blessing Shehachayenu during the circumcision and does not make the blessing during the redemption, but when the child is exempt from being redeemed, he does not make the blessing Shehachayenu.

9The Father of a son, stands over the mohel to let [the mohel] know that he is [acting as] the father’s agent.

12It is customary to have a meal on the day of the circumcision. Rema: And it is customary to assemble a minyan [i.e., a quorum of ten] for the circumcision meal, and it is considered a “mitzvah meal." And anyone who does not participate in a mitzvah meal are like those outcast by God, but only if honest/worthy people are [in attendance] there. But if dishonest/unworthy people are [in attendance at the mitzvah meal], one is not obligated to eat there. It is also customary to make a meal and a feast on the Friday night after the birth of a son, and for people to come and partake [of food] near the baby. This is also a mitzvah meal.

13On the day of a circumcision that falls on a public fast day, those called up to the Torah read the selichot (penitential prayers) and recite the vidui (confession of sins) as usual, but they do not say "V'hu rachum" (a liturgical phrase meaning "But He is merciful") nor do they perform nefilat apayim (prostrating themselves). (However, they do say "El erech apayim" - "God, patient and merciful.") (Beit Yosef in the name of Rashba)