The Ancient Irish Epic Tale Táin Bó Cúalnge

Cuchulain agrees to allow the Connacht host to continue their march on condition that every day they send one of their champions to meet him in single combat. When he shall have killed his opponent, the host shall halt and pitch camp until the following morning. Medb agrees to abide by these terms. In each of the contests which ensue, the heroic youth is victorious and slays many of the most celebrated warriors on the side of Connacht. The severest of all these single combats was the one in which he had as opponent his former friend and foster-brother Ferdiad. At the end of a four days' battle, in which both adversaries exhibited astounding deeds of valour, Ferdiad fell by the hands of Cuchulain.

Impatient at these delays, Medb broke the sacred laws of ancient Irish chivalry and led her army into Ulster, overrunning the province, pillaging and burning as she went, even up to the walls of Emain Macha, the residence of Conchobar, and finally took possession of the Brown Bull of Cualnge.