John 14:9:

Jesus saith unto him, Have I been so long time with you, and yet hast thou not known me, Philip? he that hath seen me hath seen the Father; and how sayest thou then, Shew us the Father?

See also:

How to See God’s Will Concerning Healing
The SAME Test
Objection: It’s up to God – God Will Heal Me If He Wants To
Objection: God ALLOWS Sickness, But Never More Than He Gives You Grace to Endure
Objection: Belief in God’s Sovereignty over Sickness and Suffering Has Proven a Tremendous Comfort to Countless Christians Through the Ages
Notes on Psalm 145:8-9