For the controversy is not merely as regards the [paschal] day, but also as regards the form itself of the fast. For some consider themselves bound to fast one day, others two days, other still more, while others do so during forty...And this variety among the observers of the fasts had not its origin in our time [i.e., mid-second century A.D.], but long before in that of our predecessors, some of whom probably, being not very accurate in their observance of it, handed down to posterity the custom as it had, through simplicity or private fancy, been introduced among them. And yet nevertheless all these lived in peace one with another, and we also keep peace together. Thus, in fact, the difference in observing the fast establishes the harmony of our common faith.
—St. Irenaeus, Fragments from the Lost Writings of Irenaeus, III.