(14) باب بَيَانِ تَفَاضُلِ الإِسْلاَمِ وَأَىِّ أُمُورِهِ أَفْضَلُ
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.
Reference: Sahih Muslim 39
In-book reference: Book 1, Hadith 67
USC-MSA web (English) reference(deprecated numbering scheme): Book 1, Hadith 63