Abdullah bin 'Amr bin Al-'as (May Allah be pleased with them) reported:
A man asked the Messenger of Allah (ﷺ): "Which act in Islam is the best?" He (ﷺ) replied, "To give food, and to greet everyone, whether you know or you do not."[Al-Bukhari and Muslim]. (JA)
App reference (JA): Book 6, Hadith 1 (JA)
Arabic/English book reference (JA): Book 6, Hadith 845 (JA)