Musannaf Ibn Abi Shayba 28:1109

Waki’ narrated to us, he said: Sufyan narrated to us, from Hajjaj bin Abi Yazid, from Mujahid, who said: The Messenger of Allah (peace and blessings of Allah be upon him) was asked about a man who travels alone. He said: "A devil." It was said: "And two?" He said: "Two devils." It was said: "And three?" He said: "A company."