Prayer
A recited incantation designed to force or cajole a deity or deities into changing the normal, existing, or probable course of events in the universe, obtain an advantage, or avoid a divine penalty. Also an expression of gratitude or adulation, or an affirmation of continual fear, made to a deity.

A prayer is often accompanied by a promise or a sacrifice (the firstborn, money, giving up a favorite vice, not lying, a select bit of food the priests can eat) to seal or satisfy the agreement. A spell.