From Longman Dictionary of Contemporary Englishfire in your bellyfire in your bellya strong desire to achieve something Ali returned to boxing with a new fire in his belly. → fire
Examples from the Corpus
fire in your belly• It stung the back of her throat and fired in her belly.• Three years later, he returned; heavier, slower, but with a new kind of fire in his belly.• You have got the fire in your belly that will make an excellent detective novel. 