La Genèse 17:12 Halakha : Mishneh Torah, Circumcision

Circumcision is an affirmative precept, the neglect of which entails the penalty of excision, as it is said, "And the uncircumcised male who is not circumcised in the flesh of his foreskin—that soul shall be cut off from his people" (Gen. 17:14). It is a duty incumbent upon the father to circumcise his son, and upon the master to circumcise his male slave, whether "born in the house" or bought with money. If the father or master failed to perform the circumcision, he has neglected the fulfillment of an affirmative precept but has not incurred the penalty of excision, to which only the uncircumcised person is made liable. In such case of neglect, the court is charged with the duty of circumcising the infant or slave at the appointed time, and must not leave any male uncircumcised among the Israelites or their slaves.

The master is under an obligation to circumcise his male slaves, whether at birth they were his property or whether they had been acquired from a non-Israelite. There is a distinction however between these cases. A slave born in an Israelite's home is circumcised on the eighth day after birth; the slave bought with money, on the day that he is bought. Even if he was born on the day he was bought, he is circumcised on the same day.

Circumcisions are only performed during the daytime after sunrise, whether the operation takes place on the eighth day, the regular time, or subsequently, from the ninth day and further on, as it is said "on the eighth day" (Gen. 17:12) i.e. by day, and not at night. If the circumcision takes place after daybreak, it is correct. The whole of the day is proper for circumcision. Still it is a duty to perform it in the early part of the day, for the zealous fulfill their religious obligations at the earliest possible time.