3 “This was now,” he says, “the third time that Jesus showed Himself to His disciples after that He was risen from the dead.” And this we are to refer not to the manifestations themselves, but to the days (that is to say, taking the first day when He rose again, and the [second] eight days after, when the disciple Thomas saw and believed, and [the third] on this day when He so acted in connection with the fishes, although how many days afterwards it was that He did so we are not told); for on that first day He was seen more than once, as is shown by the collated testimonies of all the evangelists: but, as we have said, it is in accordance with the days that His manifestations are to be calculated, making this the third; for that [manifestation] is to be reckoned the first, and all one and the same, as included in one day, however often and to however many He showed Himself on the day of His resurrection; the second eight days afterwards, and this the third, and thereafter as often as He pleased on to the fortieth day, when He ascended into heaven, although all of them have not been recorded in Scripture.
Source: Tractates on the Gospel of John (New Advent)