Aided Lóegairi Búadaig

Background information

The History of Ireland (Geoffrey Keating), Volume 2
pp. 211-213 Conchubhar had a poet called Aodh son of Ainneann, who carried on an intrigue with Maghain, Conchubhar’s wife; and when Conchubhar discovered this, the judgment he passed on the poet was that he be drowned in Loch Laoghaire; and at the king’s command a company went with him to drown him. And when Laoghaire Buadhach’s steward saw this, he went to Laoghaire and said that there was no place in Ireland where the poet could be drowned but at his own door.
Thereupon Laoghaire leaped out, and his poll struck against the upper door-post of the house, and his skull was broken; after this he made a sudden onslaught on the company, and slew them, and rescued the poet; and he himself died on the spot. Such was the end of Laoghaire Buadhach.

Related poem online: Fianna batar i n-Emain
Whitley Stokes (ed. & tr.), “On the deaths of some Irish heroes,” Revue Celtique, 23, 1902, pp. 303-348.
Digital Edition at Archive.org (pp. 303-348)
The death of Lóegaire Búadach (See Section 2), q. 14, p. 307, p. 320, p. 325, p. 335

List of Historic Tales in the Book of Leinster includes:
Aided Loegaire (The Tragical Death of Laeghaire), p. 588 (624)

Cóir Anmann: Fitness of Names (Stokes), Irische Texte, Ser. III.2
Loegaire Birnn Buadach §218 (See Section 1), p. 377, p. 421

Wikipedia
Ulster Cycle
Conchobar mac Nessa; Kings of Ulster
Lóegaire Búadach
Mugain