Rule 417.1.e.1

Only Valid Damage is Dealt. Example: A unit reads “when I take damage, give me +2 [M] this turn.” A spell is played that Prevents the next 3 damage the unit would take. If a player plays Hextech Ray targeting the unit, it will take no damage and its triggered ability will not trigger. If that player had played Void Seeker instead, it would be Dealt 1 and trigger its ability.