Numbers 23:19:

God is not a man, that he should lie; neither the son of man, that he should repent: hath he said, and shall he not do it? or hath he spoken, and shall he not make it good?

See also:

Forgiven People Can Be Healed
Forever Settled
Job Explained
Bible-Believing Churches That Don’t Believe the Bible
Objection: We Cannot Demand Healing from God Because God Is Sovereign
Objection: Saying, “I Am Healed” When You Are Actually Sick Is Lying, and Therefore Sin
Objection: You Never Know What God Will Do