Origen — on Josh 5:13 (HOMILIES ON NUMBERS 27.11)

“And so you must beware and exercise great care in order to discern with knowledge the kinds of visions, just as Joshua the son of Nun, when he saw a vision and knew there was temptation in it, immediately asked the one who appeared to him and said, "Are you for us, or for our adversaries?" So, then, the soul progresses when it comes to the place where it begins to distinguish between visions; and it is proved to be spiritual if it knows how to discern them all. That is why, as well, one of the spiritual gifts, given by the Holy Spirit, is mentioned as "the ability to distinguish between spirits."”