Mukhtasar Bukhari (Abridged) 2059 — Greet everyone, whether known

Narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that a man asked the Messenger of Allah (peace and blessings of Allah be upon him), "Which deed of Islam is the best?" He (peace be upon him) replied: "Feeding (the needy) and greeting everyone—those whom you know and those whom you do not know, in short, greeting all (Muslims)."