The Elder Scrolls: Tamriel

This ring can store up to 5 levels of spells. When found, it holds 1d6 - 1 levels of GM-chosen spells. A creature can store a 1st–5th level spell by casting it into the ring while touching it; the spell takes no effect and uses space equal to its level. If there's not enough space, the spell is lost. While attuned, you can cast stored spells using the original caster's stats. Once cast, the spell is expended and frees up space in the ring.