Cú Ruí was told that a single man had been holding the four great provinces of Ireland in check from the Monday at the beginning of Samain until the beginning of spring. He was grieved by this and he thought that his people had been without him for too long, so he came forward to do battle and combat with Cú Chulainn.
Cú Ruí went forward then to the men of Ireland and when he got there, he saw Amairgin lying on his left elbow to the west of Tailtiu. Cú Ruí came to the north of the men of Ireland. His people furnished him with stones and rocks and great flagstones and he began to hurl them directly against Amargin so that the warlike battle-stones collided in the clouds and in the air over their heads and each stone was shattered into a hundred pieces. ‘By the truth of your valour, Cú Ruí’ said Medb, ‘cease from this stone- throwing, for it is no help to us but a hindrance’. ‘I swear’ said Cú Ruí, ‘that I shall not cease till the day of doom until Amargin cease too’. ‘I shall do so’, said Amargin, ‘and do you undertake not to come again to help and succour the men of Ireland’. Cú Ruí agreed to that and went away to his own land and his own people.
By this time they had gone westwards past Tailtiu. ‘It was not the agreement I made’ said Amargin, ‘not to cast stones at the host again’. So he came to the west of them and turned them before him to the north-east past Tailtiu and began to pelt them for a long time.
Then said the men of Ireland that it would be no dishonour for Amargin if they vacated the encampment and the hosts went back a day's journey northwards holding themselves in check, and that Amargin should cease to attack the hosts until he came to them on the day of the great battle where the four great provinces of Ireland would meet at Gáirech and Ilgáirech in the battle of the Foray of Cúailnge. Amargin agreed to that and the hosts withdrew a day's journey northwards once more.
That is Oislige Amargin in Tailtiu.