Maliks Muwatta Book 54, Hadith Number 35.

Section : Travelling Alone in the case of Men and Women.

Malik related to me from Abd ar-Rahman ibn Harmala from Amr ibn Shuayb from his father from his father that the Messenger of Allah, may Allah bless him and grant him peace, said, “One rider is a shaytan. Two riders are two shaytans, and three are a riding-party.”