The Answer of Dionothus
The Answer of [Dionothus,] the Abbot of Bangor, to Augustino the monk, requiring subjection to the Roman church, about the year 603; in Welsh and English; (word for word) : out of Spelman's Concilia*
Bid yspys a diogel i chwil, yn bod ni holl un ac arall yn uvydd ac ynn ostyngedyg i Eglwys Duw ac ir paab o Ruvain, ac i bool kyur grissdion dwyvol, i garu pawb yn i radd mewn kariad perffaith, ac i helpio pawb, o honaunt a gair a gweithred i vod ynn blant i dduw : ac amgenach uvyddod no hwn nid adwen i vod ir neb ir yddych chwi yn henwi yn baab ne yn daad o daade yw gleimio ac yw ovunn. Ar yvydddod hwn ir yddym ni yn barod yw roddi ac yw dalu iddo ef, ac i pop krisdion yn dragwyddol. Hevyd in ydym in dan ly wodraeth esgob Kaerllion ar Wysc yr hwn ysydd yn olygwr dan dduw arnobm ni y wneuthud i ni gadwyr ffordd ys brydol.
Be it known and certain to you, that we are all and singular obedient and subject to the church of god and to the pope of Rome, and to every pious christian, to love every one in his degree with perfect charity, and to help every one of those, and by workd and deed, to be the sons of god : and other obedience than this I know not due to him whom you name the pope, or the father of fathers to challenge and to require. But this obedience we are ready to give and pay to him, and to every christian for ever. Moreover we are under the government of hte bishop of Caerleon upon Usk, who is superintendent under god over us to make us keep the spiritual way.
Spelmen, Henry. Concilia, decreta, leges, constitutiones in re ecclesiarum orbis britannici (1636). referenced in: The life of King Arthur: from ancient historians and authentic documents. ed. by Joseph Ritson. London: Payne and Foss, 1825.
I can't trace this text back further than Spelmen, and even then I do not have a copy of his book. The language is far too late for Old Welsh, of course; but where Spelmen got it, or whether he made it up, I do not know. There are any number of "charter" books for parishes, and it may come from a late one--though pre-Reformation--one.
Dionoth is mentioned in Holinshed's Chronicles in this context, but I can't find any other mention of him.