Fled Bricrenn/Bricrend (Bric(c)riu’s Feast), in Lebor na hUidre (Book of the Dun Cow). Twelfth Century AD (c AD 1106), originally Eighth Century AD:

Henderson, George, ed and tr. Fled Bricrend: The Feast of Bricriu (An Early Gaelic Saga Transcribed from Older MSS into the Book of the Dun Cow, by Moelmuiri mac mic Cuinn na m-Bocht). London: David Nutt, 1899.
https://ia803209.us.archive.org/13/items/fledbricrendfeas02hend/fledbricrendfeas02hend.pdf