Waki' bin al-Jarrah وكيع بن الجراح · 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."