Source: TW
The shaiva-s originally conceptualized rudra-sadAshiva as panchamantra-tanu, i.e., one whose body is made up of 5 mantra-s. The pancharAtra has two variations of this theme. viShNu is said to assume this 5-fold form, pancha-mUrti of viShNu, when “refracted” through his five shakti-s: parameShThinI, puruShi, vishvA, nivR^itti and sarvA. These shakti-s constitute the equivalent of the panchamantra-tanu of viShNu and are the source of prakR^iti:
pa
ncha-shaktimayo devah paramAtmA jagat-prabhuh |nchendriya-samAyogah panchadhA j~nAnam ashnute ||
pa
(parama-saMhitA)
One of them is the vaiShNava panchabrahma seen in some early pAncharAtrika tantra-s like the aShTAdasha-vidhAna. The second is the tradition of the parama-saMhitA and pAdma-saMhitA, which says the five-fold form of viShNu is specified by the panchopaniShan-mantra-s. These mantra-s are known as parameShThin, puruSha, vishva, nivR^itti and sarva with their respective bIja-s. The pAdma-saMhitA specifies the mahAbhiSheka of viShNu with the panchagavya-s using these mantra-s.