Lash of the Spelldrinker

Alter: You gain a +1 bonus to attack and damage rolls made with this magic weapon. While attuned to this whip, you are considered proficient with it and can use it as a spellcasting focus. In addition, you can use your spellcasting ability modifier for any attack and damage roll made with it, instead of Strength or Dexterity.

When a hostile creature within the whip's reach casts a spell, you can use your reaction to make a weapon attack against that creature with the whip. On a hit, the target must make a saving throw using its spellcasting ability against your spell save DC. On a failed save, you learn the level of the creature's highest remaining spell slot, and the creature takes extra force damage equal to that number.

When a creature takes force damage from the whip in this way, you can choose to recover an expended spell slot of a level equal to or less than the force damage dealt, up to 3rd level. Once the whip has been used to recover a spell slot in this way, it can't do so again until the next dusk.

Attunement: Spellcaster
Rarity: Rare
Type: Whip
Cost: 3285gp

Griffons Saddlebag, Vol II

very rare variant (no spell recovery limiter)