How Rome Came to Fast on the Sabbath

But some people in some countries of the West, and especially in the city, not knowing the reason for this allowance, think that a release from fasting certainly ought not to be granted on the Sabbath. They say that on this day the apostle Peter fasted before his encounter with Simon. But from this it is quite clear that he did it not by a canonical rule but because of the needs of his coming struggle. For there, too, for the same purpose, Peter seems to have laid on his disciples not a general fast but a special one, which he certainly would not have done if he had known that it was customarily kept by canonical rule. Just so, he would surely have been ready to appoint it even on Sunday, had the occasion of his struggle fallen on that day. Yet no canonical rule of fasting would have been made general from this, because no general observance led to it, but a necessity, which forced it to be kept on a single occasion. [a]