In one God, externally existent and manifested in three persons: Father, Son, and Holy Spirit. 

Deuteronomy 6:4 
Hear, O Israel: The LORD our God, the LORD is one.

Matthew 28:19-20
Therefore go and make disciples of all nations, baptizing them in[a] the name of the Father and of the Son and of the Holy Spirit, and teaching them to obey everything I have commanded you. And surely I am with you always, to the very end of the age.

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.

Titus 3:4-6
But when the kindness and love of God our Savior appeared, he saved us, not because of righteous things we had done, but because of his mercy. He saved us through the washing of rebirth and renewal by the Holy Spirit, whom he poured out on us generously through Jesus Christ our Savior.