Fisting and God's Will
"Before attempting fisting, a Christian husband and wife should pray together and ask for divine guidance. The husband should ask that God guide his hand and work through him, and for the skill and patience to fist his wife correctly and maximize her pleasure. The wife should pray for openness and readiness to receive God’s love and grace in the form of her husband’s hand."
Subtopics of this article include, "The Fist of Might", "Powerful yet Gentle", "Fisting as an Act of Faith" and "Role Reversal".
Full article here.
ETA:
And while you're there, don't forget to check out the entries on anal sex and BDSM!