Kelley's "The Ancestry of Eve of Leinster" (The Genealogist, 1980) XII:2.
On 7 Jan 1996, Stewart L Baldwin posted to the soc.genealogy.medieval newsgroup on Internet in which he pointed out that this Cas was a bogus ancestor invented in the time of BRIAN BORU to give his family a link to the illustrious EOGAN MOR.