Narrated 'Abdullah bin 'Amr:

A person asked Allah's Messenger (ﷺ) . "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."

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