What is the earliest reference available for the fundamental belief in worshiping Prana? Where is it documented the belief that Prana created the world?
AtharvaVeda Samhita contains Prana Sukta in 11.4 which glorifies Prana:
Homage to Prāna, him who hath dominion o'er the universe, Who hath become the Sovran Lord of all, on whom the whole depends!
Prāna is Fever, he is Death. Prāna is worshipped by the Gods. Prāna sets in the loftiest sphere the man who speaks the words of truth.
Prāna is Deshtri, and Virāj Prāna is reverenced by all. He is the Sun, he is the Moon. Prāna is called Prajāpati.