I thought it would be helpful to list the earliest triadic formulae with reference to the divine in Christian literature. They show considerable variety in what names are mentioned together, their relative order, and the theological conception. The liturgical use of such formulae in doxologies, benedictions, and baptismal discourse is likely older than their use in theological/doctrinal elaboration. The early use of triadic formulae is thus an important ingredient to the christological development that led to the Trinity doctrine. I have marked with (***) the texts where the three are mentioned in rather strict parallelism.
PAULINE AND SUB-PAULINE LITERATURE
1 Corinthians 12:4-6: "There are different kinds of gifts, but the same Spirit. There are different kinds of service, but the same Lord. There are different kinds of working, but the same God works all of them in all men". (Spirit < Lord < God)***
2 Corinthians 1:21: "Remember it is God himself who assures us all, and you, of our standing in Christ, and has anointed us, marking us with his seal and giving us the pledge, the Spirit, that we carry in our hearts". (God < Christ < the Spirit)
2 Corinthians 13:14: "May the grace of the Lord Jesus Christ, and the love of God, and the fellowship of the Holy Spirit be with you all". (Lord Jesus Christ < God < Holy Spirit)***
Romans 15:30: "But I beg you, by our Lord Jesus Christ, and the love of the Spirit, to help me through my dangers by praying to God for me". (Lord Jesus Christ < the Spirit < God)
2 Thessalonians 2:13: "But we feel that we must be continually thanking God for you, brothers whom the Lord loves, because God chose you from the beginning to be saved by the sanctifying Spirit". (Lord < God < santifying Spirit)
Ephesians 1:3: "Praise be to God the Father of our Lord Jesus Christ, who has blessed us in the heavenly realms with every blessing of the Spirit in Christ". (God the Father < Lord Jesus Christ < the Spirit)
Ephesians 2:18, 22: "Through him [Christ Jesus], both of us have in the one Spirit, our way to come to the Father ... All grow into one holy temple in the Lord; and you too, in him, are being built into a house where God lives, in the Spirit". (him < one Spirit < the Father; the Lord < God < the Spirit)
Ephesians 4:4-6: "There is one body and one Spirit, just as you were called to one hope when you were called, one Lord, one faith, one baptism, one God and Father of all, who is over all and through all and in all". (Spirit < Lord < God and Father)***
MATTHEAN/Q COMMUNITY
Matthew 28:18-19: "Then Jesus came to them and said, 'All authority in heaven and on earth has been given to me. Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit' ". (Father < Son < Holy Spirit)***
Didache 7:1-3: "Concerning baptism, baptize thus: Having first rehearsed all these things, baptize in the name of the Father and of the Son, and of the Holy Spirit, in running water; but if you have no running water, baptize in other water, and if you cannot in cold, then in warm. But if you have neither, pour water three times on the head in the name of the Father, Son, and Holy Spirit". (Father < Son < Holy Spirit)***
JOHANNINE COMMUNITY
John 14:16-17: "I shall ask the Father, and he will give you another Paraclete to be with you for ever, the Spirit of Truth whom the world can never accept". (I < the Father < Paraclete/Spirit of Truth)
John 14:26: "The Paraclete, the Holy Spirit, whom the Father will send in my name, will teach you everything". (Paraclete/Holy Spirit < the Father < my name)
1 John 3:23-24: "We believe in the name of his Son Jesus Christ, and we love one another as he told us to. Whoever keeps his commandments lives in God and God lives in him. We know that he lives in us by the Spirit that he has given us". (Son Jesus Christ < God < the Spirit)
Odes of Solomon 19:1-4: "A cup of milk was offered to me, and I drank it in the sweetness of the Lord's kindness. The Son is the cup, and the Father is he who was milked, and the Holy Spirit is she who milked him. Because his breasts were full, it was undesirable that his milk should be released without purpose. The Holy Spirit opened her bosom, and mixed the milk of the two breasts of the Father." (Son < Father < Holy Spirit)***
Odes of Solomon 23:21-22: "And the letter became a large volume, which was entirely written by the finger of God. And the name of the Father was upon it, and of the Son and of the Holy Spirit, to rule forever and ever. Hallelujah". (Father < Son < Holy Spirit)***
OTHER CATHOLIC EPISTLES
Hebrews 9:14: "How much more effectively the blood of Christ, who offered himself as the perfect sacrifice to God through the eternal Spirit, can purify our inner self". (Christ < God < the eternal Spirit)
1 Peter 1:2: "Peter, apostle of Jesus Christ, sends greetings to all those ... who have been chosen, by the provident purpose of God the Father, to he made holy by the Spirit, obedient to Jesus Christ and sprinkled with his blood" (God the Father < the Spirit < Jesus Christ)
CLEMENT OF ROME
1 Clement 46:6: "Have we not one God, and one Christ, and one Spirit of grace poured upon us?". (God < Christ < Spirit of Grace)***
1 Clement 58:2: "Receive our counsel, and there shall be nothing you you to regret, for as God lives and as the Lord Jesus lives and the Holy Spirit, the faith and hope of the elect, he who with lowliness of mind and eager gentleness has without backsliding performed the decrees and commandments given by God shall be enrolled and chosen in the number of those who are saved through Jesus Christ, through whom is to him the glory forever and ever. Amen". (God < Lord Jesus < Holy Spirit)***
IGNATIUS OF ANTIOCH
Ephesians 9:1: "I have learned, however, that some from elsewhere have stayed with you, who have evil doctrine; but you did not suffer them to sow it among you, and stopped your ears, so that you might not receive what they sow, seeing that you are as stones of the temple of the Father, made ready for the building of God the Father, carried up to the heights by the engine of Jesus Christ, that is the cross, and using as a rope the Holy Spirit". (God the Father < Jesus Christ < Holy Spirit)***
Magnesians 13:1: "Be diligent therefore to be confirmed in the ordinances of the Lord and the Apostles, on order that 'you may prosper in all things whatever you do' in the flesh and in the spirit, in faith and love, in the Son and the Father and the Spirit, at the beginning and at the end". (Son < Father < the Spirit)***
POLYCARP OF SMYRNA
Martyrdom of Polycarp 14:3: "For this reason, I also praise you [the Father] for all things, I bless you, I glorify you through the everlasting and heavenly High Priest, Jesus Christ, your beloved Child, through whom be glory to you with him and the Holy Spirit, both now and for the ages that are to come. Amen". (you < Jesus Christ < the Holy Spirit)***
JUSTIN MARTYR
1 Apology 61: "In the name of God, the Father and Lord of all, and of our Savior, Jesus Christ, and of the Holy Spirit, they then receive the washing with water". (God the Father < Savior Jesus Christ < Holy Spirit)***
1 Apology 67: "For all the favors we enjoy we bless the Creator of all, through His Son Jesus Christ and through the Holy Spirit." (Creator of all < Son Jesus Christ < Holy Spirit)***
SECOND-CENTURY EXTRACANONICAL WRITINGS
Testament of Isaac 1:1: "In the name of the Father, the Son, and the Holy Spirit, the One God." (Father < Son < Holy Spirit)***
Testament of Isaac 8:7: "He [Jesus] is the one to whom are due the glory, the dignity, the majesty, the dominion, the reverence, the honor, the praise, and the adoration, along with the merciful Father, and the Holy Spirit now and for all time, and to all eternity and forever and ever, amen!" (Jesus < Father < Holy Spirit)***
Epistula Apostolorum 5: ? ?What meaning is there in these five loaves?? They are a picture of our faith concerning the great Christianity; and in the Father, the ruler of the entire world, and in Jesus Christ our Saviour, and in the Holy Spirit, the Paraclete, and in the holy Church and in the forgiveness of sins.? (Father < Jesus Christ our Savior < Holy Spirit)***
Sybilline Oracle 7.66-70: "You did not recognize your God, whom the Jordan washed in its streams, and the Spirit flew like a dove. He, before earth or starry heaven, was sovereign Word, with the Father and Holy Spirit". (Word < Father < Holy Spirit)***
There is also the parody of the Father, Son, and Holy Spirit in Revelation 13:1-18 in the Dragon, the First Beast, and the Second Beast (the False Prophet), and the triadic thought in 1 John 5:6-7 and 1 Corinthians 13:13.