Augustine of Hippo

(Tr. xxx. s. 4) As if He said, Ye have done well to receive circumcision from Moses, not because it is of Moses, but of the fathers; for Abraham first received circumcision from the Lord. And ye circumcise on the sabbath. Moses has convicted you: ye received a law to circumcise on the eighth day; and ye received a law to rest on the seventh day. If the eighth day after a child is born happen to be the sabbath, ye circumcise the child; because circumcision appertaineth to, is a kind of sign of, salvation; and men ought not to rest from the work of salvation on the sabbath.