Contrapositive

The contrapositive: if he were not a true prophet, he would seek worldly benefit from his claims. But he rejected every offer: Quraysh's wealth offers, kingship proposals, compromise suggestions. He chose persecution, poverty, and hardship over comfort. He died with his armor pawned to a Jewish merchant. His actions are the exact opposite of what a false prophet would do.

This is proof by contrapositive: instead of proving "true prophet → rejects worldly gain" directly, we observe "rejected worldly gain → true prophet." The complete absence of self-interest confirms authenticity.