"Assalamu alaikum" is a common greeting among Muslims, meaning "Peace be with you." It is an Arabic phrase, but Muslims from around the world use this greeting, regardless of their language background.
The appropriate response is "Wa alaikum assalaam" (And upon you be peace.)
Pronunciation
as-salam-u-alay-koom
Alternate Spellings
salaam alaykum, assalaam alaykum, assalaam alaikum, and others
Variations
• "Assalamu alaikum wa rahmatullah" (May the peace and mercy of Allah be with you)
• "Assalamu alaikum wa rahmatullahi wa barakatuh" (May the peace, mercy, and blessings of Allah be with you)
The Quran reminds believers to reply to a greeting with one of equal or greater value: "When a courteous greeting is offered you, meet it with a greeting still more courteous, or at least of equal courtesy. Allah takes careful account of all things" (4:86). These variations are used to extend the level of the greeting.
Origin
This universal Islamic greeting has its roots in the Quran. As-Salaam is one of the Names of Allah, meaning "The Source of Peace." In the Quran, Allah instructs the believers to greet one another with words of peace:
"But if you enter houses, salute each other - a greeting of blessing and purity from Allah. Thus does Allah make clear the signs to you, that you may understand" (24:61).
"When those come to you who believe in Our signs, say: 'Peace be upon you.' Your Lord has inscribed for Himself the rule of mercy" (6:54).
Further, the Quran describes that "peace" is the greeting that angels will extend to believers in Paradise.
“Their greeting therein will be, 'Salaam!'” (Quran 14:23).
“And those who kept their duty to their Lord will be led to Paradise in groups. When they reach it, the gates will be opened and the keepers will say, 'Salaam Alaikum, you have done well, so enter here to abide therein'” (Quran 39:73).
(See also 7:46, 13:24, 16:32)
Traditions
The Prophet Muhammad used to greet people with "Assalamu alaikum," and encouraged his followers to do so as well. This helps bond Muslims together as one family, and establish strong community relationships. The Prophet Muhammad once advised his followers to observe five rights that a Muslim has over his brother/sister in Islam: greeting each other with "salaam," visiting them when they're sick, attending their funerals, accepting their invitations, and asking Allah to have mercy on them when they sneeze.
It was the practice of early Muslims that the person who enters a gathering should be the first one to greet the others. It is also recommended that a person walking should greet a person who is sitting, and a younger person should be the first to greet an older person. When two Muslims argue and cut off ties, the one who reestablishes contact with a greeting of "salaam" receives the greatest blessings from Allah.
The Prophet Muhammad once said: “You will not enter Paradise until you believe, and you will not believe until you love one another. Shall I tell you about something which, if you do it, will make you love one another? Greet each other with Salaam" (Sahih Muslim).