What diverts the command in the verse from Surat An-Nisa (Chapter of Women): "then greet with a better greeting than it" from obligation to recommendation, if it is permissible to suffice in returning the greeting by saying: "Wa Alaikum Assalam (And upon you be peace)," when the one who gives the greeting completes his greeting with its best formulations?

Responding to a greeting (Salam) is obligatory, and anything added to a similar response is commendable. If the one greeting says, "As-salamu alaykum" (Peace be upon you), it is permissible to restrict the reply to "Wa alaykum as-salam" (And upon you be peace). It is better to add "wa rahmatullah" (and the mercy of Allah) or "wa rahmatullahi wa barakatuh" (and the mercy of Allah and His blessings). If the one greeting says, "As-salamu alaykum wa rahmatullahi wa barakatuh," then responding in kind is obligatory, according to His 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]. Indeed, Allah is ever, over all things, an Accountant." (Quran 4:86). Thus, responding in kind is obligatory, and adding more is recommended. It is not permissible to restrict the reply to "Wa alaykum as-salam" in this case. However, if the one greeting adds more than "wa rahmatullahi wa barakatuh," the reply should be limited to "Wa alaykum as-salamu wa rahmatullahi wa barakatuh" because that is what the Sunnah brought. Some jurists have interpreted responding in kind, in the case of adding to "As-salamu alaykum," as referring to the most complete form. Therefore, it is permissible to restrict the reply to "Wa alaykum as-salam" even if the one greeting adds "wa rahmatullah."