One time there was in Mag nAilbe a great council of the peoples of Ireland, among whom there was great contention throughout the year between the new Easter and the old Easter. Laisrén of Lethglinn and his followers advocated the new Easter and new rite, but the remaining elders of Ireland praised the old Easter and old rite. Saint Fintán did not immediately arrive at this council, and all the peoples were waiting for him. For he was the leader and chief of those who advocated the old Easter. Then Suibne son of Domnall, king of the Uí Bairrche, [said]:
‘Why are you waiting so long for that leprous cleric? Even if he comes, Laisrén's Easter will prevail until Judgement Day’.
Laisrén said to him:
‘Be quiet, for Fintán hears what you say in the place in which he is, and you will be punished by him’.
On that day, before evening, Fintán arrived at the council, and he and Laisrén exchanged greetings. When king Suibne had asked Fintán for a blessing, Fintán said to him:
‘Why do you ask for a blessing from a leprous cleric? When you uttered an insult against me Christ, [sitting] on the right of God the Father, blushed with shame, because I am a true limb of Christ. You will therefore die before the harvest is gathered, and your brothers will slay you, and your blood will be mixed with buttermilk, and your head will be cast into the river Barrow and will never be seen again’.
And this was fulfilled. For in that month his nephew slew him by the little river called Blathach, and his head was left behind in the river Barrow.