And the evidence that those travelers who are fewer than three are sinners is that the Prophet, peace and blessings be upon him, informed that one is a devil, and two are two devils, and it is likely that the meaning of his saying: "a devil" or "a sinner" is like His saying: "devils of mankind and jinn" (__QUR_6:112__), and its meaning is: sinners among the jinn and mankind.
Sayyiduna Amr bin Al-As (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "A single (traveler) is a devil, and two travelers are two devils, and three people are a caravan and a group."
Hadith Referenceصحيح ابن خزيمه / كتاب: المناسك / 2570