Musannaf Ibn Abi Shayba 28:875

Waki’ narrated to us, from al-A’mash, from Abu Wa’il, who said: A letter from ‘Umar reached us while we were in Khanaqin: "If a man says to a man, 'Do not enter,' he has granted him safety. If he says, 'Do not fear,' he has granted him safety. And if he says, 'Mutarras' (you are protected/shielded), he has granted him safety." He said: "Allah knows the languages."