Souldrinking

Book of Vile Darkness 3.5
By Monte Cook 

This melee weapon bestows one negative level each time it deals damage normally. When the wielder scores a critical hit with the weapon, it bestows two negative levels, and the wielder gains +1d8 temporary hit points and a +2 enhancement bonus to Strength. The temporary hit points and enhancement bonus fade after 1 hour.

Caster Level: 17th; Prerequisites: Craft Magic Arms and Armor, energy drain; Market Price: +4 bonus.