It is narrated from Sayyiduna Abdullah bin Amr (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Worship the Most Merciful, feed (others), spread the greeting of peace, you will enter the gardens (of Paradise)."
Benefits and Issues: From the aforementioned narrations, it is understood that spreading the greeting of salam generally brings safety and well-being in this world and the Hereafter, and it is also a means of entering Paradise. It promotes mutual love; therefore, one should greet even the person whom one does not know.
Source: Fadlullah al-Ahad: Urdu Commentary on al-Adab al-Mufrad, Page: 981