The Epistle to Diognetus

But again their scruples concerning meats, and their superstition relating to the Sabbath and the vanity of their circumcision and the dissimulation of their fasting and new moons, I do [not] suppose you need to learn from me, are ridiculous and unworthy of any consideration.

For of the things created by God for the use of man to receive some as created well, but to decline others as useless and superfluous, is not this impious?

And again to lie against God, as if He forbad us to do any good thing on the Sabbath day, is not this profane?

Again, to vaunt the mutilation of the flesh as a token of election as though for this reason they were particularly beloved by God, is not this ridiculous?

And to watch the stars and the moon and to keep the observance of months and of days, and to distinguish the arrangements of God and the changes of the seasons according to their own impulses, making some into festivals and others into times of mourning, who would regard this as an exhibition of godliness and not much more of folly?

That the Christians are right therefore in holding aloof from the common silliness and error of the Jews and from their excessive fussiness and pride, I consider that thou hast been sufficiently instructed; but as regards the mystery of their own religion, expect not that thou canst be instructed by man.