The Whispering Promise

The Whispering Promise is an uncommon Ring that grants a bonus to Attack Rolls and Saving Throws to creatures healed by the wearer.

A soft, soothing voice floats from this ring, reciting a prayer over and over.

Properties

The wearer of this item gains:

Blessed Mercy: When you heal a creature, it gains a +1d4 bonus to  Attack rolls and  Saving throws for 2 turns.

Volo does not trade via dialogue at the Sacred Pool. One must click the trade button in the lower left while speaking with him to do so. The ring can also be stolen.
This ring can only be bought or stolen from Grat if it was not previously acquired from Volo. It is the same ring, confiscated from Volo when he is captured.
If Volo is rescued and joins the party's camp, he sells the ring there if it was not previously acquired from him or Grat. Additionally, Grat no longer sells the ring after Volo leaves the Goblin Camp, even if Volo later dies or leaves the party's camp.

Regarding Blessed Mercy:

Applies the same condition as the standard  Bless spell, and therefore cannot stack with it.
- Despite also being called  Bless, this buff is not enhanced by the  Staff of Arcane Blessing.
Multi-target healing abilities, such as  Mass Healing Word or a thrown  Potion of Healing, bless all affected creatures (potentially including the caster).
Drinking a  Potion of Healing counts as healing oneself and triggers the effect of the ring as well.
The Bless effect is applied even if the target being healed is already at full health.
Healing effects from the  Ring of Regeneration,  Helm of Balduran, or taking a Short Rest all count as healing oneself and trigger the effect of the ring as well.
The self-healing from Life Domain Cleric's  Blessed Healer does not trigger the effect.
Gaining temporary hit points does not count as healing and therefore does not trigger the effect.