The reference is to the Pastor or Shepherd of Hermas, a work of the second century. The passage to which Cassian alludes is found in Book II. Commandm. vi.; where it is said that “there are two angels with a man, one of righteousness and the other of iniquity,” and suggestions are given how to recognize each of them and to distinguish the suggestions of the one from those of the other. The passage is also alluded to by Origen, De Principiis, Book III. c. ii. and Hom. xxxv. in (Lucam); and Cassian refers to it again in Conf. XIII. c. xii.