The Holy Prophet (S) said: "When you meet each other then initiate greeting (salam) and embrace; and when you separate from each other, then depart with seeking forgiveness."
Bihar-ul-Anwar, vol. 76, p. 4
Imam Husayn-ibn-’Ali (‘a) said: "Seventy rewards is the share of the one who initiates a 'greeting' and only one reward belongs to the one who returns the 'greeting'." (When two people see each other, the initiator of the exchange of greetings receives a greater reward.)
Bihar-ul-Anwar, vol. 78, p. 120
Imam as-Sadiq (‘a) said that the Messenger of Allah (S) gathered the children of 'Abd-il-Muttallib and said: "O' children of 'Abd-il-Muttallib! Initiate greetings, have regard for kinship, perform the night prayers while people are asleep, feed (others) food, and deliver good speech and thereby you will enter paradise in peace."
Bihar-ul-Anwar, vol. 69, p. 393
Imam as-Sadiq (‘a) said: "He who initiates a greeting is more beloved with Allah and His Messenger."
Wasa'il-ush-Shiah vol.12, p. 55