Acolyte's Reward is a uncommon Instant card from Born of the Gods (BNG), collector number 1. Current market price: $0.15 (foil $0.36), TCGplayer market prices via Scryfall.
Prevent the next X damage that would be dealt to target creature this turn, where X is your devotion to white. If damage is prevented this way, Acolyte's Reward deals that much damage to any target. (Each {W} in the mana costs of permanents you control counts toward your devotion to white.)