Is it permissible to say "peace and mercy of Allah" in response to a greeting, and is one rewarded for doing so?

It is recommended for a Muslim to return a greeting better than what was given, or at least similarly, based on the Almighty's saying: (And when you are greeted with a greeting, greet [in return] with one better than it or [at least] return it [in a like manner]). Saying "Peace and Allah's Mercy" instead of "And upon you be peace" is considered sufficient, but it is contrary to what is superior, as it is better to use the full formula with "upon you" (عليكم). Defining "peace" (السلام) in the response is recommended but not obligatory, and using the definite article (ال) is preferable.