H20 the earliest of earliest christians believe in the trinity, the eastern orthodox are a prime example of this. As did jesus make revealing refferences to God's triune nature... we are to be baptized "in the name of the father, the son and the holy spirit". But then again, you'd just rub it off as corruption while in the same breath you seek islamic prophecies in the same claimed 'corrupted' gospels.
All heretics that denied trinity like arius, muhammed, charles taze russell all came afterwords !! and had little or no knowledge about early christian tradition.
While all the early church fathers who were rooted out of the disciples of the apostles too the jews or the disciples of Paul too the gentiles. Believed in the trinity as is the nature of the trinity all over the bible and cannot be ignored or overlooked. All heretics that didn't believe in a trinity, had nothing to do with christianity, they came later, they changed the message of the gospel and they are the ones that altered texts and theology of the bible.
If i had to make a report on a car accident, i'd rather trust those that were there when it happend, then some guy who comes 5 hours later after it happend when the streets cleaned up and the car is towed away saying that he knows how it really happend.
By the way funny, you give the link to an URL wich explains the trinity as being ONE God. something you arrogantly do not wish to understand but since you've read this site, cleary know how the trinity is to be perceived.
And nowhere does it say that it wasn't believed back then, it's all over the new testament! And of course the word "trinity" isn't mentioned by name, that's only a theological name given to it by Tertullianus 200 years after jesus's life. But the trinity was believed troughout the christian world since it's very dawn, excluding the early heretics of course (wich appeared only later in gnostic, coptic or greek communities).
Because a name isn't mentioned doesn't mean it isn't in there. Tertullianus could of coined it whatever he wanted and we would of repeated it today, the name doesn't matter. That's like saying if a person doesn't call the sun, nova, then the sun doesn't excist... because the sun only excists if you coin it nova.
So if you'd look for "sun" in scripture, you'd only recognize it where it would read nova and overlook where it really was mentioned out of ignorance. In a same way you seek trinity in scripture and overlook where it really shows. Bad reasoning muslim friend.