Is it permissible to offer the greeting of peace with the words "peace be upon you" and what is the ruling on one who does so?

There is no harm in initiating a greeting with the phrase "Salamun 'alaykum" (peace be upon you) or "Salamun 'alayka" (peace be upon you, singular), and the one who does so will be rewarded. This form appears in the Holy Quran as the greeting of the angels to the people of Paradise. Scholars have differed on which is better between "Al-Salamu 'alaykum" and "Salamun 'alaykum," but the correct view is that both are permissible.

What is disliked in greeting is to initiate it by saying " 'Alayka al-salamu" (upon you be peace) or " 'Alaykum al-salamu" (upon you be peace, plural); because it is the greeting of the dead. The intent is that poets and others used to greet the dead with this phrase, not that the Sunnah for greeting the dead is in this manner. Otherwise, the Sunnah of the Prophet, peace be upon him, in greeting the dead is like his Sunnah in greeting the living, by offering the salutation first.

The most complete form of greeting is for the Muslim to say: "Al-Salamu 'alaykum wa rahmatullahi wa barakatuh" (Peace be upon you, and the mercy of Allah, and His blessings), or "Salamun 'alaykum wa rahmatullahi wa barakatuh." As for adding "wa maghfiratuh" (and His forgiveness) or "wa ridwanuh" (and His good pleasure), it is not correct.