Didache 16
Then the human race will come into the fire of testing. Many will stumble and be ruined, but those who hold out in their faith will be saved by the Curse-bearer himself.
And then the signs of the truth will appear: first a sign of opening in heaven, then a sign of a trumpet blast, and third the rising of the dead — not of all, but as it was said: “The Lord will come, and all the holy ones with him.”
Then the world will see the Lord coming on the clouds of heaven.
Greek
τότε ἥξει ἡ κτίσις τῶν ἀνθρώπων εἰς τὴν πύρωσιν τῆς δοκιμασίας, καὶ σκανδαλισθήσονται πολλοὶ καὶ ἀπολοῦνται, οἱ δὲ ὑπομείναντες ἐν τῇ πίστει αὐτῶν σωθήσονται ὑπ᾽ αὐτοῦ τοῦ καταθέματος. καὶ τότε φανήσεται τὰ σημεῖα τῆς ἀληθείας· πρῶτον σημεῖον ἐκπετάσεως ἐν οὐρανῷ, εἶτα σημεῖον φωνῆς σάλπιγγος, καὶ τὸ τρίτον ἀνάστασις νεκρῶν· οὐ πάντων δέ, ἀλλ᾽ ὡς ἐρρέθη· Ἥξει ὁ κύριος καὶ πάντες οἱ ἅγιοι μετ᾽ αὐτοῦ. τότε ὄψεται ὁ κόσμος τὸν κύριον ἐρχόμενον ἐπάνω τῶν νεφελῶν τοῦ οὐρανοῦ.