As-Salaam is a name amongst the names of God, which He sent down on earth. Therefore, spread Salaam amongst yourselves. Verily when a Muslim passes by a group of people and says Salaam to them and they reply, the one who initiates Salaam, pets a degree of excellence over the people who were offered Salaam. If they do not reply then Angels, who are superior to humans, give a reply to the one who offered Salaam

As-Salaam is a name amongst the names of God, which He sent down on earth. Therefore, spread Salaam amongst yourselves. Verily when a Muslim passes by a group of people and says Salaam to them and they reply, the one who initiates Salaam, pets a degree of excellence over the people who were offered Salaam. If they do not reply then Angels, who are superior to humans, give a reply to the one who offered Salaam

REFERENCE:  http://muntakhabahadith.com