Sahih al-Bukhari 28
صحيح البخاري#28SahihNarrated '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
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 2:21