In Srimad Bhagavatam, King Nimi asks nine yogiswaras questions about the qualities of bhagavatas and also about how a bhagavata should worship the Supreme One. One of the yogiswaras was Avirhotra. He told Nimi that he should worship Kesava through Tantras. By the word tantra, the Pancharatra Agama is indicated, said P.T. Seshadri in a discourse.
There are two sets of Vaishnava Agamas — Vaikhanasa and Pancharatra. Here, Avirhotra tells Nimi to worship according to Pancharatra, which is also known as tantra, according to the Paadma Samhita. The Paadma Samhita also uses the words moola mantra, Satvata and Bhagavat Sastra for Pancharatra. Avirhotra says that one should learn the method of worship through an Acharya. Once he has studied under an Acharya, then he can worship a murthi of his choice, says Avirhotra. He says the devotee should worship through moola mantra, and by this is meant the Ashktakshara mantra.
Because Pancharatra was told by Lord Narayana, it is called Bhagavat Sastra. He taught the Pancharatra to Brahma, in the course of five nights, and hence the name. He taught Brahma one and a half crore granthas, and He later taught the same to five sages in different sacred places, where they received instruction from the Lord. Each of the sages was an amsa of the Lord’s weapons. Sage Sandilya was an amsa of His chakra and he was taught in Melkote. Aupakayana was an amsa of His conch and he was taught in Vanamamalai. Mounchyayana, an amsa of the Lord’s mace, studied from the Lord in Tiruvanantapuram; Kausika, an amsa of His bow studied in Srimushnam and Bharadwaja, an amsa of His sword, studied in Salagrama.