2 Timothy 4:2:

Preach the word; be instant in season, out of season; reprove, rebuke, exhort with all longsuffering and doctrine.

See also:

The Baseball Diamond of Healing
Preparing to Minister Healing
Healing and the Fear of the Lord
I Have an Engagement to Preach Healing Somewhere, But I’m Really Sick Myself!  What Should I Do?
Objection: Paul Left Trophimus at Miletum Sick Instead of Healing Him