John Chrysostom, Homilies on 1 Corinthians 29 (discernment)
Therefore they also received discernings of spirits, so as to discern and know who speaks by a pure spirit and who by an unclean one. For it was not possible to give proof of the things said on the spot — prophecy does not furnish the test of its own truth at the time it is spoken, but at the time of the outcome…
And the prophet is not like the diviner, but with sober mind and self-control and composure, knowing what he utters, he says everything. So even before the outcome you may recognize from this the diviner and the prophet.
Greek
Διὸ καὶ διακρίσεις ἔλαβον πνευμάτων, ὥστε διακρίνειν καὶ εἰδέναι, τίς μὲν ὁ πνεύματι φθεγγόμενος καθαρῷ, τίς δὲ ὁ ἀκαθάρτῳ. Ἐπειδὴ γὰρ αὐτόθεν οὐκ ἦν παρασχεῖν τῶν λεγομένων τὴν ἀπόδειξιν· προφητεία γὰρ οὐκ ἐν τῷ καιρῷ, ᾧ λέγεται, ἀλλ’ ἐν τῷ καιρῷ τῆς ἐκβάσεως παρέχεται τῆς οἰκείας ἀληθείας τὸν ἔλεγχον… Ὁ δὲ προφήτης οὐχ οὕτως, ἀλλὰ μετὰ διανοίας νηφούσης καὶ σωφροσύνης καὶ καταστάσεως, καὶ εἰδὼς ἃ φθέγγεται, ἅπαντά φησιν. Ὥστε καὶ πρὸ τῆς ἐκβάσεως κἀντεῦθεν γνώριζε τὸν μάντιν καὶ τὸν προφήτην.