"We know that the old man does not suffer harm from them but we. . . ."

"One day Abba Sisoes left Abba Anthony's mountain to go to the outer mountain of the Thebaid and there he stayed.  Now there were some Meletians there who lived at Calamon of Arsinoe.  Hearing that the old man had come to the outer mountain, some people wished to see him but they said, 'What shall we do because the Meletians are on the mountain.  We know that the old man does not suffer harm from them but we are afraid lest, in wanting to meet the old man, we fall into the temptation of the heretics [(πειροσμὸν τῶν αἱρετικῶν)].'  So as not to meet the heretics, they did not go to see the old man."

Abba Sisoes 48 (PG 65, col. 405/406).  This one doesn't appear in the Collection systématique (SC 387, 474, and 498), or, at least, not in the Concordance (SC 498, pp. 217 ff.) under Sisoès.  The desert Christian: sayings of the Desert Fathers: the alphabetical collection, trans. Benedicta Ward (New York, NY:  Macmillan Publishing Co., Inc., 1975), 221, italics mine.  (The Melitians were more schismatics than heretics, however.)