1. Rasulullah (SAW) said,
“You will not enter Jannah until you have perfect Imaan, and you do not have perfect Imaan until you have love and brotherhood amongst yourselves, should I not show something, if you act upon it you will love each other – make abundant and spread salaam amongst each other.” (Sahih Muslim)
2. Rasulullah (SAW) said,
“Certainly the person close to Allah Ta’ala is the one who initiates salaam.” (i.e. makes salaam first) (Mishkaat)
3.Anas (R.A.) says Rasulullah (SAW) said to me
"O my son when you enter your home, make salaam, it will be a source of blessing for you and for your household. "(Tirmizi)
4. Rasulullah (SAW) said,
“Salaam is before speech.” (Mishkaat)
Commentry
The unique and universal greeting of Islam has been taught and encouraged to us by Rasulullah (SAW). Making salaam to each other regularly builds a strong bond of love and brotherhood amongst Muslims. It also helps in killing off the maladies of pride, ostentation and avarice. Today many of us tend to greet only those who we know whereas in one Hadith it is reported, you should greet the one you know and who you don’t. Some people are shy to use the complete greeting of salaam and rather suffice with the word “salaam” only. This is incorrect. The words of salaam taught to us by the Hadith are Assalaamu Alaykum Wa Rahmatullahi Wa Barakaatuh .
Rasulullah (SAW) has exhorted us to spread greetings by salaam, which will strengthen our brotherhood and reap blessings. To answer someone who has greeted with salaam is compulsory. This applies to letters, e-mails etc.