Williams, H. (1899) Two Lives of Gildas by a monk of Ruys and Caradoc of Llancarfan Cymmrodorion Record Series, pp.120.

The Ruys Life is 11th C. or earlier, the Caradoc life 12th C.
The Lives are both online at Mary Jones' site.
For a discussion of the Lives, see Robert Vermaat's Summary.