Bannian is an archaic term for a member of the vanika in the Indian caste system - a trader or merchant belonging to the business class. The Bannians feature in the book A voyage to Suratt: in the year, 1689 by J Ovington, M.A. Chaplain to His Majesty. Ovington describes the Bannians as humble, innocent and patient, refraining from ‘hot words.’ He notes that they have the greatest respect for all kinds of beasts, especially cows, and consider even the killing of a fly a crime.
The Critical review: or, Annals of literature, Volume III, published in 1804, describes the Bannians as loving everything that breathes, assisting everything that is in pain, abhorring the spilling of blood, and abstaining from food that has enjoyed life. They restrict their diet to milk, butter, cheese, rice and vegetables. This veneration for all creatures is the 'superstition' Fielding refers to.