Genesis 17:26

In the selfsame day was Abraham circumcised, and Ishmael his
son.
] This is repeated, that it might be taken notice of that both were circumcised according to the command of God, and on the very day in which it was given. Jarchi observes, it was in the day, and not in the night; which shows, says he, he was not afraid of the Heathen, and of mockers; and that his enemies, and the men of that generation, might not say, if we had seen him, we would not have suffered him to be circumcised, and keep the commandment of God: and some of the Jewish writers ^F5 fable, that he was circumcised on the day afterwards appointed by Moses for the day of atonement, and that in the place where he was circumcised the altar was built; but all this is without any foundation. This affair was transacted, according to Bishop Usher {f}, A. M. 2107, and before Christ 1897.