Hadith 17:436
Abu al-Ahwas narrated to us, from Abu Ishaq al-Harith, from Ali, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The Muslim has [a right] over the Muslim: he should greet him with peace when he meets him."
حدثنا أبو الأحوص عن أبي إسحاق الحارث عن علي قال قال رسول الله صلى الله عليه وسلم للمسلم على المسلم يسلم عليه إذا لقيه