Finally found it in the bible, thanx to http://www.bible.org; I think.
So it's true... it's from the bible, you didn't know it and I didn't know that. Here it comes:
Marcus 5,9:
Than He asked him: What is thou name?
He answered:
"My name is Legion, for I am many"
The whole story:
They came in the land of the Gerasenen. When He stepped out of the boot, a man came out of the caves who had a bad spirit in him. He ran towards Jezus, he shouted:
What do you have to do with me, Jezus, Son of God, the Allmighty? I tell you by God; don't torture me!
Because He had told him: Bad spirit, be gone!
Than He asked him: What is thou name?
He answered: My name is Legion, for I am many
....
Read the bible for the correct passage...