score:1
Eusebius preserves much of the relevant history prior to his time.
Circa AD 190 a controversy arose regarding the date on which the Lord's Passover should be observed:
A question of no small importance arose at that time. For the parishes of all Asia, as from an older tradition, held that the fourteenth day of the moon, on which day the Jews were commanded to sacrifice the lamb, should be observed as the feast of the Saviour's passover. It was therefore necessary to end their fast on that day, whatever day of the week it should happen to be. But it was not the custom of the churches in the rest of the world to end it at this time, as they observed the practice which, from apostolic tradition, has prevailed to the present time, of terminating the fast on no other day than on that of the resurrection of our Saviour.
Synods and assemblies of bishops were held on this account, and all, with one consent, through mutual correspondence drew up an ecclesiastical decree, that the mystery of the resurrection of the Lord should be celebrated on no other but the Lord's day, and that we should observe the close of the paschal fast on this day only... (HE 5.23.1-2)
Eusebius records that Irenaeus was crucial in mediating the controversy:
- Among them was Irenaeus, who, sending letters in the name of the brethren in Gaul over whom he presided, maintained that the mystery of the resurrection of the Lord should be observed only on the Lord's day... (HE 5.24.11)
"The mystery of the resurrection of the Lord should be observed only on the Lord's day" is about as close as we're going to get to "Resurrection Sunday" in the ancient world.
(keeping in mind that although the first day of the week was indeed named for the sun, this was hardly a term that was comfortable for early Christians living under Roman pagan rule. Sun worship was pagan. Justin (see First Apology ch. 67) acknowledges Christians worshipping on the day that was called Sunday--that's what the Romans called it--but he himself eschewed their pagan customs. "Resurrection Sunday" is a natural simplification of Irenaeus' statement, once Christians were comfortable using the word "Sunday").