From the Sunan of meeting a Muslim are the following:
The Messenger of Allah salAllahu ‘alayhi wa sallam was asked, “Which Islam is good (in terms of actions?” He said, “To feed the people and to say Salaam to those you know and those you do not know.”
Lengthen the Greeting:
A man entered upon the Messenger of Allah salAllahu ‘alayhi wa sallam and said, “As-salaamu alaykum.” The Messenger salAllahu ‘alayhi wa sallam replied to the Salaam. Then the man sat down and the Messenger said, “Ten.” Then another man came and said, “As-salaamu alaykum wa rahmatullah.” The Messenger salAllahu ‘alayhi wa sallam replied. Then the man sat down and the Messenger said, “Twenty.” Then another came and said, “As-salaamu alaykum wa rahmatullahi wa barakatuh.” The Messenger salAllahu ‘alayhi wa sallam replied. Then the man sat down and the Messenger said, “Thirty.”
[No evidence for saying the Salaam when entering or leaving the Masjid was found. However, what is confirmed in the Sunnah is to pray two Rak’ah of Tahiyaat Al-Masjid on entering. For more details check the Sunnah of Masjid post]
Look at how much loss of reward a person inflicts on himself by sufficing himself with saying only a part of the salutation. The person should say the entire Salaam so that he attains thirty good deeds. The least reward for a good deed is ten times its like; therefore, by saying the full greeting one can earn three hundred good deeds or more. Accustom yourself to completing the Salaam up to Barakatuh to obtain this great reward.
The Muslim says the Salaam many times during the day. He says it when entering the Masjid to the people sitting and when leaving them, entering and leaving his house, etc.
Do not forget that it is also from the Sunnah that whoever decides to leave a person that he should say the complete Salaam.
The Prophet salAllahu ‘alayhi wa sallam said,
“When one of you comes to a gathering then say, ‘Salaam,’ and if someone decides to leave, then say, ‘Salaam,’ and the first does not have more right than the last.”
[It means that it is as important to give Salaam when leaving a gathering, as it is when entering it. So one does not have more right than the other.]
Smile, as the Prophet salAllahu ‘alayhi wa sallam said:
“Do not consider any of the good things as insignificant – even if it is that you meet your brother with a cheerful face.”
Shake hands, as the Prophet salAllahu ‘alayhi wa sallam said:
“There are not two Muslims who meet each other and shake hands except that they are forgiven before they depart (from each other).”
Imam An-Nawawi said, “Knowing that this shaking of hands is preferred with every meeting.”
Notice that if you shake hands with whomever you meet, greet them with Salaam and smile at them you would have fulfilled three Sunan at once.
[It is not permissible to shake hands with a non-Mahram.]
Say a Kalimah Tayyibah:
The Prophet salAllahu ‘alayhi wa sallam said, “A Kalimah Tayyibah [goodly word] is charity.” Kalimah Tayyibah includes the remembrance of Allah, supplication, Salaam, praising someone for their good traits, noble character, good manners and actions.
A Kalimah Tayyibah has a powerful affect on a person – it brings peace and tranquility to a person’s soul and puts serenity into his heart. It is evidence of what is in the heart of the believer of light, guidance and proof of being on the right path.
Have you thought, my dear, to fill your life – from the morning to the evening – with kind words to your spouse, children, neighbors, friends, co-workers and whomever else you deal with, who maybe in need of such words?