Yes, it is true that buttering toast before putting it in the toaster can be a fire hazard. Butter is a highly flammable substance, and when it comes into contact with the heating elements inside the toaster, it can easily catch fire.
Toasters are designed to toast dry bread, and they are not intended to handle any kind of spread or topping. When butter is applied to the bread before toasting, it can drip down into the toaster and come into contact with the hot heating elements or electrical components, leading to a potential fire.
In addition to the fire hazard, putting buttered toast in the toaster can also cause damage to the toaster and create difficult-to-clean messes. It is best to avoid buttering or adding any spread to the bread before toasting and instead, apply toppings after the toasting process is complete. If you want to add butter or other toppings to your toast, it's safer to do so manually after the toast has popped up from the toaster.