'Abdullah bin 'Amr bin Al-'as (May Allah be pleased with them) reported:
A man asked Messenger of Allah (ﷺ), "Which act in Islam is the best?" He (ﷺ) replied, "To feed (the poor and the needy) and to greet those whom you know and those you do not know."[Al-Bukhari and Muslim].
Arabic/English book reference: Book 1, Hadith 550