The only way there can be faith for healing,
is for there to be a promise of healing from
God in the Bible (which is his will).

"He sendeth is Word and healeth them and
delivered them from their destructions"
Psalms 107:20

". . . .the word of God which effectually
worketh " in them that believe, and is "health
to all their flesh." 1 Thessalonians 2:12 and
Proverbs 4:22