For the controversy is not merely as regards the day, but also as regards the form itself of the fast. For some consider themselves bound to fast one day, others two days, others still more, while others [do so during] forty: the diurnal and the nocturnal hours they measure out together as their [fasting] day. And this variety among the observers [of the fasts] had not its origin in our time, 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. And the presbyters preceding Soter in the government of the Church which you now rule— I mean, Anicetus and Pius, Hyginus and Telesphorus, and Sixtus— did neither themselves observe it [after that fashion], nor permit those with them to do so. Notwithstanding this, those who did not keep [the feast in this way] were peacefully disposed towards those who came to them from other dioceses in which it was [so] observed although such observance was [felt] in more decided contrariety [as presented] to those who did not fall in with it; and none were ever cast out [of the Church] for this matter.
On the contrary, those presbyters who preceded you, and who did not observe [this custom], sent the Eucharist to those of other dioceses who did observe it. And when the blessed Polycarp was sojourning in Rome in the time of Anicetus, although a slight controversy had arisen among them as to certain other points, they were at once well inclined towards each other [with regard to the matter in hand], not willing that any quarrel should arise between them upon this head. For neither could Anicetus persuade Polycarp to forego the observance [in his own way], inasmuch as these things had been always [so] observed by John the disciple of our Lord, and by other apostles with whom he had been conversant; nor, on the other hand, could Polycarp succeed in persuading Anicetus to keep [the observance in his way], for he maintained that he was bound to adhere to the usage of the presbyters who preceded him.
And in this state of affairs they held fellowship with each other; and Anicetus conceded to Polycarp in the Church the celebration of the Eucharist, by way of showing him respect; so that they parted in peace one from the other, maintaining peace with the whole Church, both those who did observe [this custom] and those who did not.
Source: Fragments from the Lost Writings of Irenaeus (New Advent)