The Standard Book of Spells
The Unbreakable Vow is a magical incantation in which one wizard makes an oath to another. If the oath is broken, the consequence to the agreeing party is death. To create an Unbreakable Vow, two wizards must stand facing each other, holding hands, with a third wizard, designated ‘Bonder’ who will cast the spell. Upon consent of the Vow, a tongue of fire wraps around the hands of the wizards.