That the Messenger of Allah ﷺ said: "If the people knew what I know about being alone, then a rider would not journey at night." - meaning alone.  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ لَوْ أَنَّ النَّاسَ يَعْلَمُونَ مَا أَعْلَمُ مِنَ الْوَحْدَةِ مَا سَرَى رَاكِبٌ بِلَيْلٍ يَعْنِي وَحْدَهُ  

The Messenger of Allah ﷺ said: A single rider is a devil, and a pair of riders are a pair of devils, but three are a company of riders.  

قَالَ رَسُولُ اللَّهِ ﷺ الرَّاكِبُ شَيْطَانٌ وَالرَّاكِبَانِ شَيْطَانَانِ وَالثَّلاَثَةُ رَكْبٌ  

The Prophet ﷺ said: When three are on a journey, they should appoint one of them as their commander.  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ إِذَا خَرَجَ ثَلاَثَةٌ فِي سَفَرٍ فَلْيُؤَمِّرُوا أَحَدَهُمْ  

The Prophet ﷺ said: The best number of companions is four, the best number in expeditions four hundred, and the best number in armies four thousand; and twelve thousand will not be overcome through smallness of numbers. Abu Dawud said: What is correct is that this tradition is mursal (i.e. the link of the Companion is missing).  

عَنِ النَّبِيِّ ﷺ قَالَ خَيْرُ الصَّحَابَةِ أَرْبَعَةٌ وَخَيْرُ السَّرَايَا أَرْبَعُمِائَةٍ وَخَيْرُ الْجُيُوشِ أَرْبَعَةُ آلاَفٍ وَلَنْ يُغْلَبَ اثْنَا عَشَرَ أَلْفًا مِنْ قِلَّةٍ