1 Corinthians 9:16:

For though I preach the gospel, I have nothing to glory of: for necessity is laid upon me; yea, woe is unto me, if I preach not the gospel!

See also:

Sickness as Chastening and Judgment in the New Testament
Healing and Obedience
Objection: Jonah Was Brought to the Point of Death So That He Would Learn Obedience
Mistake: Disobedience