Matthew incorporates this line, albeit with an asterisk as reminder to the reader that the earliest manuscripts did not contain these words.
Luke does not have the doxology at all.
So where did this liturgical addition come from?
1 Chronicles 29:10-13?
"Then David blessed the Lord in the presence of all the assembly; David said: ‘Blessed are you, O Lord, the God of our ancestor Israel, for ever and ever. Yours, O Lord, are the greatness, the power, the glory, the victory, and the majesty; for all that is in the heavens and on the earth is yours; yours is the kingdom, O Lord, and you are exalted as head above all. Riches and honor come from you, and you rule over all. In your hand are power and might; and it is in your hand to make great and to give strength to all. And now, our God, we give thanks to you and praise your glorious name."
This collection of early apostolic teachings prescribes disciples gathered and scattered thrice daily to recite this prayer, including the doxology.
There are probably as many suggestions as there are stars in the sky for the origin of the doxology that concludes the traditional rendition of Jesus' Prayer. Regardless of where the doxology comes from, the lyric is critical for liturgical, theological, and related missional purposes.
True. Jesus may not have said it when initially asked about how to pray. After all, he needed no reminders in regards to whom the kingdom, the power, and the glory belonged.
But I do.
The church does.
We all do.
Maybe that's why it was added later, lest we forget.
As I have worked through this late arrival to the Abba Prayer,  much of my reflections have been guided by Jan Milič Lochman. The Czech theologian delivered an address to the World Alliance of Reformed Churches in 1982, "Thine Is the Kingdom, and the Power and the Glory," and his words continue to echo relevance throughout a world saturated in unjust kingdoms, graceless powers, and quests for glory no matter what the cost.
So I find it best, as I muse about the doxology, to simply throw out a few snippets from the address and add my own commentary 30 years after these words were initially spoken in Ottawa, Ontario.