Mac Datho's Hound
From Ancient Irish Tales, edited by Tom P Cross and Clark Harris Slover, Barnes & Noble 1936, reprinted 1996:
"There was a famous land-holder of Leinster. Mac Datho (Son of the Two Mutes) was his byname. He had a hound that would run round all Leinster in one day. That hound's name was Ailbe, whence the Plain of Ailbe is called. And of him was said:
"Mesroida was Mac Datho's name,/ Who had the pig - no falsehood!/ And Ailbe, his famous cunning splendid hound,/ From whom is the renowned plain of Ailbe."
Now Ireland was full of the fame and renown of that hound. Then to Mac Datho came messengers from Medb and Ailill of Connacht to ask him for his hound. But at the same time came messengers of Ulster and Conchobar to ask for the same hound. ..."
From this beginning unwinds "The Story of Mac Datho's Pig", written probably in the 9th or 10th century.