Before Vishnu had a temple. Before the ocean of milk was churned. Before the Puranas were written down at all.
There was a text called the Shatapatha Brahmana.
It is a difficult, technical, extraordinary book — a manual of Vedic ritual, mostly, embedded in the Yajurveda, concerned with the exact construction of fire altars and the precise chanting of syllables. It is not the kind of book…