1 John 2:1:

My little children, these things write I unto you, that ye sin not. And if any man sin, we have an advocate with the Father, Jesus Christ the righteous:

See also:

Healing Is Not on a Case-by-Case Basis
Mistaken Prayer Mindsets
If You Blow It
Am I Sick Because an Unanswered Accusation Has Been Brought Against Me in a Heavenly Court?
Objection: Teaching Grace Gives People a License to Sin