1 Thessalonians 2:13:

For this cause also thank we God without ceasing, because, when ye received the word of God which ye heard of us, ye received it not as the word of men, but as it is in truth, the word of God, which effectually worketh also in you that believe.

See also:

Who You Are and What You Have
You’re Not an Exception
God’s Word Is Seed
Trust the Word to Work
The Insecure Preacher
If God Hears Our Faith-Filled Prayers for Healing Immediately, Why Does Our Healing Not Manifest Immediately?
I Believed I Received My Healing When I Prayed, but My Body Doesn’t Act Like It.  They Called a Healing Line.  Should I Get into It or Not?
Is ”Seeing Yourself Healed” a New Age Visualization Technique?