Musannaf Ibn Abi Shayba 37:580

Waki’ narrated to us, from Yahya ibn Abi al-Haytham, from Yusuf ibn Abdullah ibn Salam, from his father, who said: "Do not unsheathe your swords, for if you unsheathe them, they will not be sheathed until the Day of Resurrection." And he said: "Wait for me for eighteen," meaning the day of Uthman.