There is. Nevertheless, the matter was not settled definitively until the year 325 A.D. at a Church Council.
I believe that the passage in Genesis constitutes a reference to the Trinity. This interpretation has a long tradition in Christian history. But the Jews, to this day, regard the passage as a reference to God and the angels.
The two things that come to mind is when the Pharisees asked Christ if he was the Son of God, and he answered them saying, "I am." Christ also stated that He and His Father were one.
But there is no direct reference to Christ, The Father and The Holy Spirit being one, is there? Nevertheless, the command to "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" should suffice as proof.
Nor is Christ's dual nature immediately obvious from these passages. Arianism was a very widespread heresy at one time in the history of the Church.
Just a clarification - When Jesus said "I AM", he was using the same name that God gave Moses when Moses asked who should he say had sent him.
Don't agree? The Jews Jesus was talking to thought so - they picked up rocks to stone him. They knew EXACTLY what he was claiming - to be the great "I AM".
That depends on the translation you're using. 1 John 5:7-8 may or may not contain a phrase known as the "Johannine Comma" which reads: "...in heaven, the Father, the Word, and the Holy Ghost: and these three are one. And there are three that bear witness in earth...."
The full text of these verses with the Johannine Comma included reads: "For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one. 8 And there are three that bear witness in earth, the Spirit, and the water, and the blood: and these three agree in one."
There is disagreement as to whether this phrase is a legitimate part of Scripture however. I'm not sure whether it is included in Catholic translations or not.