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The doctrine of the Trinity is encapsulated in Matthew 28:19, where Jesus instructs the apostles: "Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit."

"Go ye therefore, and teach all nations, ~~baptizing them in the name of the Father, and of the Son, and of the Holy Ghost.~~" Matthew 28:19 KJV
Go, and make disciples of all the nations in My Name, teaching them to observe all things whatsoever I have commanded you,” [[Matt. xxviii. 19.]]
From Proof of the Gospel (the Demonstratio) by Eusebius.
Eusebius (265-339 CE) Bishop of Caesarea around 314 CE
Book III, Chapter 7, 136 (a-d), p. 157
http://www.ccel.org/ccel/pearse/morefathers/files/eusebius_de_05_book3.htm

also
(2) Book III, Chapter 6, 132 (a), p. 152
(3) Book III, Chapter 7, 138 (c), p. 159
(4) Book IX, Chapter 11, 445 (c), p. 175
(5) Book I, Chapter 3, 6 (a), p. 20
(6) Book I, Chapter 5, 9 (a), p. 24

In ~311 CE Eusebius (265-339) Bishop of Caesarea
In his _Proof of the Gospels_
in Book three chapter seven states
Go, and make disciples of all the nations in My Name, teaching them to observe all things whatsoever I have commanded you,” [[Matt. xxviii. 19.]]
http://www.ccel.org/ccel/pearse/morefathers/files/eusebius_de_05_book3.htm
Apparently Matthew 28:19 was changed
after Eusebius wrote his Proof of the Gospel.

shalom b'SHEM Yah'shua HaMashiach

That it is the Lord only who is meant by the Father, Son, and Holy Spirit in Matthew 28:19 is evident from what there precedes and what follows. In the preceding verse the Lord says, "All power is given unto Me in heaven and on earth," and in the following verse He says, "Lo, I am with you all the days, even to the consummation of the age;" thus He speaks of Himself only, so that He spoke in that manner [about the Father, Son, and Holy Spirit] to make His disciples aware that there is a trinity in Him. Doctrine of the Lord 46:6 ~ Swedenborg