The next time a source of your choice would deal damage to you this turn, prevent that damage. If damage is prevented this way, Deflecting Palm deals that much damage to that source's controller.
9/20/2014 Deflecting Palm doesn’t target any permanent or player. You choose a source of damage as Deflecting Palm resolves.
9/20/2014 If multiple prevention and/or replacement effects are trying to apply to the same damage, the player who would be dealt damage chooses the order in which to apply them.