John 16:33:

These things I have spoken unto you, that in me ye might have peace. In the world ye shall have tribulation: but be of good cheer; I have overcome the world.

See also:

The Insecure Preacher
Objection: We Are Promised Tribulation in This World
Objection: It Is Unbalanced to Teach That Life’s Problems Are Due to a Lack of Faith
Objection: My Trials Only Come to Make Me Strong
Notes on 1 John 5:4