Sufyan bin Sa‘id Ath-Thawri سفيان الثوري · Chapters on Seeking Permission

from his father, from his grandfather, that the Messenger of Allah (ﷺ) said: "He is not one of us who resembles other than us, no who resembles the Jews nor the Christians. For indeed greeting of the Jews is pointing the finger, and the greeting of the Christians is waving with the hand."

from Abu Hurairah that the Prophet (ﷺ) said: "The young one gives the Salam to the elder, the one passing the by to the one sitting and the few to the many."