The Ring of Prayer can be bought from Licia of Lindeldt for 28,000 souls.
The Ring of Prayer increases the Faith stat by five points. This can be useful for players that want to temporarily access certain miracles or equipment that require too much Faith for their current base value. It will also boost the damage of miracles and equipment with Faith scaling.
However, it does not contribute to the level requirements for special dialogue with NPCs, such as accessing Felkin's wares or being gifted Licia's equipment. This is also true for all other stat-boosting equipment.