Warning: This is 3.0 Edition material. It is possible that there is more recent 3.5 Edition version.

Charnel Fire

(Book of Vile Darkness)

Necromancy [Evil]
Level: Cleric 5,
Components: V, S,
Casting Time: 1 minute
Range: Touch
Effect: One corpse
Duration: Instantaneous
Saving Throw: None (Will negates for undead)
Spell Resistance: No (Yes for undead)

With sinister flame and brimstone, the caster completely consumes one dead body so that absolutely nothing remains.
A creature whose body is destroyed by a charnel fire spell can only be brought back to life through a true resurrection spell.
If this spell is cast upon a corporeal undead, the creature gets a Will saving throw, and the caster must overcome its spell resistance (if any).
If the undead creature fails its save, it is destroyed forever.