It’s necessary to recognize that the earliest complete (extant) Gospel of Matthew dates from about 325, the time of the Council of Nicea. It appears that the verse describing the Trinity baptismal formula was added at that time.
Eusebius, the 4th century Church historian, had an old library available to him. His earlier references to Matt 28:19 do not contain this formula and read differently than the extant copy we have today.
The Text of the New Testament, Randall Duane Hughes
godglorified.com/matthew_2819.htm
“Within the past hundred years there have been those who brought evidence against the Mathew 28:19 Trinity baptism formula. Men such as F.C. Conybeare, K. Lake, J. Martineau, A. Harnack, A.S. Peake, H. Kosmala, etc. Conybeare is believed to have been the first to write against it, following the discovery of a variant reading of the verse, within the writings of Eusebius of Caesarea.
Some 17 times in his works prior to Nicea, Eusebius quotes Matthew 28:19 as “Go and make disciples of all nations in my name” without mentioning the Trinity baptism command. In his writings after the council of Nicea, the traditional form including the Trinity baptism formula is found 5 times, although most of these are not above question.”
A second reference to the Trinity is found in 1 John 5:7 . But this too appears to be an interpolation.
5:7 "For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one.
Wikipedia notes that "It does not appear in the older Greek manuscripts, nor in the passage as quoted by many of the early Church Fathers. The words apparently crept into the Latin text of the New Testament during the Middle Ages, “[possibly] as one of those medieval glosses but were then written into the text itself by a careless copyist”
Ant the other hand, we do have 4 references to baptism in the name of Jesus alone in Acts of the Apostles, and another in Paul’s Epistle.
