
If you are unsure what to say to him, speak from your heart. If you still want some more structured, I came across this wonderful site, that dealt with the healing power of prayer. Many prayers can be found in them.
http://www.christianhealingprayers.com/healing_books/healing_ministries_prayers.htm
http://www.crosswalk.com/faith/prayer/prayers/a-prayer-for-personal-healing.html
Everything to the Glory of God!