What are the merits of extending greetings to people whether you know them or not, as stated by the Prophet Muhammad (peace be upon him)?
 It is narrated on the authority of 'Abdullah b. 'Amr that a man asked the Messenger of Allah (may peace and blessings be upon him) which of the merits (is superior) in Islam. He (the Holy Prophet) remarked:                      That you provide food and extend greetings to one whom you know or do not know.