Sahih Bukhari Volume 1, Book 2, Hadith Number 27

Narated By ‘Abdullah bin ‘Amr : A person asked Allah’s Apostle . “What (sort of) deeds in or (what qualities of) Islam are good?” He replied, “To feed (the poor) and greet those whom you know and those whom you don’t know.”

References

Reference: Sahih al-Bukhari 28
In-Book Reference: Sahih al-Bukhari Book 2 Hadith 21