Musannaf Ibn Abi Shaybah

It is narrated from Hazrat Abu Najeeh (may Allah have mercy on him) that a person said to Hazrat Mujahid (may Allah have mercy on him) that the Holy Prophet (peace and blessings be upon him) said: "The one who travels alone is a devil, and two who travel together are two devils." Hazrat Mujahid (may Allah have mercy on him) said: "The Holy Prophet (peace and blessings be upon him) sent Hazrat Dihyah on a journey alone, and Hazrat Abdullah and Hazrat Khabbab (two persons as well)." But Hazrat Umar (may Allah be pleased with him) said: "You should travel in a group of three, so that if one of you dies, two remain to act as his guardians. The one who travels alone is a devil, and two who travel together are like two devils."