The Messenger of Allah ﷺ said, "A lone rider is a devil, two riders are two devils, and three are a travel party."
أن رسول الله ﷺ قال: الراكب شيطان، والراكبان شيطانان، والثلاثة ركب.
Malik narrated it in the Book of Seeking Permission (36), from Abdul-Rahman bin Harmala, from Amr bin Shuayb, from his father, from his grandfather, who related it. Abu Dawud (2607) and Tirmidhi (1674) also narrated it through Malik's route.Hakim (2/102) graded it sahih through the route of Muhammad bin Ismail bin Abu Fudayk, from Abdul-Rahman bin Harmala, and said, "Sahih in isnad." Ibn Khuzayma (2570) also graded it sahih through the route of Muhammad bin Ajlan, from Amr bin Shuayb.Tirmidhi said, "This is a hasan hadith." And it is as he said, for Amr bin Shuayb and his father made the hadith hasan. That is why Ibn Hajar said in Fath al-Bari (2/53), "A hadith hasan in isnad, and Ibn Khuzayma and Hakim graded it sahih."Baghawi said, "The meaning of the hadith, in my view, is what has been related from Saeed bin Musayab, as a mursal report, from the Messenger of Allah, 'Satan has designs on one person and on two, but when they are three, he has no designs on them.'"Khattabi said, "Its meaning is that being alone and going off by oneself in the land is an act of Satan, or something that Satan urges a person toward and calls him to, and likewise two people with no third among them. But when they become three, they form a rakb, that is, a group and companionship." He said, "A person traveling alone, if he dies, has no one present to wash him, bury him, and prepare him, nor anyone with him to whom he can entrust instructions concerning his property, to carry his effects to his family and bring word of him back to them, nor anyone with him on his journey to help him with the load. But when they are three, they help one another, take turns with tasks and keeping watch, pray in congregation, and secure its reward." End of quote.His statement, "and three form a rakb," with fatha then sukun, means a group.