In his epilogue to the Félire Óengusso, written sometime after Máel Ruain's death, Óengus shows himself much indebted to his "tutor" (aite), whom he remembers elsewhere as "the great sun on Meath's south plain" (grían már desmaig Midi).

[5] Of less certain origin is the text known as the Rule of Céli Dé, which is preserved in the Leabhar Breac (15th century) and contains various instructions for the regulation and observance of monastic life, notably in liturgical matters.

It is ascribed to both Óengus and Máel Ruain, but the text in its present form is a prose rendering from the original verse, possibly written in the 9th century by one of his community.

[1] Against the practices of earlier Irish monastic movements, Máel Ruain is cited as forbidding his monks to go on an overseas pilgrimage, preferring instead to foster communal life in the monastery.

[1] They are said to include Óengus, Máel Díthruib of Terryglass, Fedelmid mac Crimthainn, king of Cashel, Diarmait ua hÁedo Róin of Castledermot (County Kildare) and Dímmán of Araid.

[1] The Annals of Ulster report under the year 792 that Máel Ruain died a peaceful death, calling him a bishop (episcopus) and soldier of Christ (miles Christi).