The angel Gabriel said to Mary, The Holy Spirit shall come upon thee, and the power of the Most High shall overshadow thee therefore that holy thing which shall be born of thee shall be called the Son of God (Luke 1:35).

Here three are mentioned, the Most High, who is God the Father, the Holy Spirit, and the Son of God:

When Jesus was baptized, Lo, the heavens were opened, and John saw the Holy Spirit descending as a dove and coming upon Him and lo, a voice out of heaven saying, This is My beloved Son, in whom I am well pleased (Matt. 3:16, 17; Mark 1:10, 11; John 1:32).

And still more plainly in these words of the Lord to His disciples:

Go ye and make disciples of all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Spirit (Matt. 28:19);

and still again in these words in John:

There are three that bear witness in heaven, the Father, the Word, and the Holy Spirit (1 John 5:7).

Furthermore, the Lord prayed to His Father, and spoke of Him and with Him, and said that He would send the Holy Spirit, and He did send it. Finally the apostles in their Epistles frequently mentioned the Father and the Son and the Holy Spirit. From all this it is clear that there is a Divine trinity, which is Father, Son, and Holy Spirit.