Panchayatana form of worship introduced by Adi Shankaracharya has assigned one element to one of the five deities in Hinduism. Vishnu is the embodiment of Aakasha Mahabhuta (ether or space). The five elements are ether/space, air, fire, water and earth. The five deities in Panchayatana form of worship are Vishnu, Mother Goddess, Ganesha, Surya and Shiva.
In this concept, the five deities are worshipped in the form of sacred stones found in five holy rivers.
Bhagavan Vishnu the embodiment of Aakasha Mahabhuta is worshipped with Saligrama found in the Gandaki River in Nepal.