Is it permissible to say: "May Allah reward everyone," or "May everyone's reward be upon Allah"?

There is no harm in saying, "May Allah reward everyone," because ajr (reward) is the recompense and requital for those who work and do good, as Allah Almighty said: "Then how excellent is the reward of the workers." Similarly, the saying, "The reward of everyone is upon Allah," means that their recompense is guaranteed with Him, based on His saying: "then his reward is due to Allah," and "so his reward is upon Allah," meaning its affirmation with Allah as an obligatory matter out of His grace.