I have read where one of, if not the first, occurrence of using this doxology is in the Didache. The Didache has a number of early Christian practises that are not found explicitly in the New Testament (i.e. particulars regarding water baptism).
As for this doxology the Didache reads as follows:
Chapter 8. Concerning Fasting and Prayer (the Lord's Prayer)
But let not your fasts be with the hypocrites; Matthew 6:16 for they fast on the second and fifth day of the week; but fast on the fourth day and the Preparation (Friday). Neither pray as the hypocrites; but as the Lord commanded in His Gospel, thus pray: Our Father who art in heaven, hallowed be Your name. Your kingdom come. Your will be done, as in heaven, so on earth. Give us today our daily (needful) bread, and forgive us our debt as we also forgive our debtors. And bring us not into temptation, but deliver us from the evil one (or, evil); for Yours is the power and the glory forever. Thrice in the day thus pray.
Interesting to me how the parts I bolded are not in the NT as such. It is not to fast 'with the hypocrites' but as the NT says 'do not be like the hypocrites' NKJV version. I believe it wasn't about the days of the week they fast but rather the way they fasted to be seen of men as holy.
And the direction to pray this prayer as stated 3 times a day. Is this a common practise anywhere today ?
This got me wondering how much current church practise is still followed by some according to the Didache as in things such as fasting 1 or 2 days prior to water baptism and other early practises.
I realize that all Christian churches today have practises not found explicitly in NT scripture. However, it seems to me, of the early church practises we read about in the NT, we all cherry pick those that are still applicable and those not. Often those not explicitly described in the NT are areas of distinction resulting in all these factions in the family of God.
Thankfully God is building His Church, even though we hold to our differences.