As we grow up in Islam, or come to know it as reverts, we learn that it is good ‘adab (etiquette), in fact required, to hail a fellow Muslim with:

As-salamu alaikum! (Arabic: ٱلسَّلَامُ عَلَيْكُمْ) [Translation: Peace be upon you]

And to return the greeting, we can say, simply:

Wa alaikum as-salam! (Arabic: وَعَلَيْكُمُ ٱلسَّلَامُ) [Translation: And unto you peace]

It is in fact good practice to return the greeting even if it is given with a sincere heart by a non-Muslim. And at the end of each salat, we greet and give respect to the angels that accompany us on either side with a salaam. 

As-salamu alaikum comes from the Arabic word salaam, which means “peace.” Salaam is derived from the same root that the word Islam comes from. The word alaikum is the word ala, which means “on,” combined with a suffix that changes the meaning into “upon you.”

It is also closely related to the Hebrew phrase shalom aleichem. Shalom aleichem also means “peace be upon you.” The words salaam and shalom are both descended from the same Semitic root also meaning “peace.”

The use of the phrase has its roots in the Quran and the Hadith, holy books in Islam. Muslims are instructed to return greetings courteously in Surah an-Nisa: 86 of the Quran. In the Hadith book Sahih al-Bukhari, Volume 8, Book 74, Number 246, Adam, newly created, greets the angels of Allah with assalamu alaikum.