Wiktionary
threefold law
n. (context Wicca English) A key tenet of Wicca establishing that magick white magick and black magick are multiplied by three and returned to whom conjures it used to warn users.
Usage examples of "threefold law".
But it may help you if you remember the other equally vital law of witchcraft, the Threefold Law.
The wiccans call it the threefold law: what you do to others comes back to you threefold.