Annales Fuldenses s.a. AD 844 (entry ascribed to Rudolf of Fulda), pp. 364.
Others hypothesise that the name "Aisso" is a corruption of the Arabic Aysun, which was the name of the son of Sulayman al-Arabi, formerly imprisoned in Aachen, but who had escaped from captivity to the Hispanic March and established himself in the region of Vic.