Didache 8:2, in its version of the Lord's Prayer, contains a doxology.
Didache 8:2 in The Apostolic Fathers, ed. Kirsopp Lake, 2 vols. (The Loeb Classical Library; Cambridge MA: Harvard University Press, 1913), 1:321 (Logos ed.)
And do not pray as the hypocrites, but as the Lord commanded in his Gospel, pray thus: “Our Father, who art in Heaven, hallowed be thy Name, thy Kingdom come, thy will be done, as in Heaven so also upon earth; give us to-day our daily bread, and forgive us our debt as we forgive our debtors, and lead us not into trial, but deliver us from the Evil One, for thine is the power and the glory for ever.”
The Greek of Didache 8:2 reads:
μηδὲ προσεύχεσθε ὡς οἱ ὑποκριταί, ἀλλʼ ὡς ἐκέλευσεν ὁ κύριος ἐν τῷ εὐαγγελίῳ αὐτοῦ, οὕτω προσεύχεσθε· Πάτερ ἡμῶν ὁ ἐν τῷ οὐρανῷ, ἁγιασθήτω τὸ ὄνομά σου, ἐλθέτω ἡ βασιλεία σου, γενηθήτω τὸ θέλημά σου ὡς ἐν οὐρανῷ καὶ ἐπὶ γῆς· τὸν ἄρτον ἡμῶν τὸ ἐπιούσιον δὸς ἡμῖν σήμερον, καὶ ἄφες ἡμῖν τὴν ὀφειλὴν ἡμῶν, ὡς καὶ ἡμεῖς ἀφίεμεν τοῖς ὀφειλέταις ἡμῶν, καὶ μὴ εἰσενέγκῃς ἡμᾶς εἰς πειρασμόν, ἀλλὰ ῥῦσαι ἡμᾶς ἀπὸ τοῦ πονηροῦ· ὅτι σοῦ ἐστιν ἡ δύναμις καὶ ἡ δόξα εἰς τοὺς αἰῶνας