J.-C. Guy, Recherches sur la tradition grecque des Apophthegmata Patrum (Subsidia hagiographica, 36; Bruxelles: Société des Bollandistes, 1962).
The book (66.5 MB) is available here.
Vienna, Österreichische Nationalbibliothek, MS K321b verso. Parchment leaf with the text of the Apophthegmata Patrum in the Sahidic dialect of Coptic (the photo was taken from the website of the Austrian National Library).
Thanks a lot for this upload!
excellent web site, very rich in information related to Coptic studies;