I used to wonder sometimes, when was a first time man started realizing they have created too may of gods by now. When was the first time someone realized there are too may rule to follow and too may of holy books to worship. There was a wonderful piece of information on net, here.

Everyone is born atheist: it is indeed as old as mankind. Some men have always disbelieved in gods or supreme powers. The only problem is that the phenomenon of atheism could not be easily described early on, as primitive languages had no way to symbolize negation, or existence. Hence saying “gods don’t exist” would be a daunting task indeed. The arrival of phonetic language changes that. Atheistic views started to emerge in India, then
Greece.

It says the first reference comes from India and its none other than rig-Veda Probably the first sign of skeptic thought comes from the Rig-Veda, a text which is thought to have been written around 1000 BC. The philosophy promoted in it could be said to be atheistic by omission, as shows us this creation hymn:

“Who knows for certain? Who shall here declare it? Whence was it born and whence came this creation? The gods were born after this world’s creation. Then, who can know from whence it has arisen? None know whence creation has arisen and whether he has or has not produced it. He who surveys it in the highest heaven, he only knows, or happily, he may know not“.

Around 500 BC, Buddhism, inspired by the Rig-Veda, became a theistic philosophy. Jainism, an atheistic religion, also began around that time.