ENOfficial
‘Abdallah b. ‘Umar reported God’s Messenger as saying, “If people knew what I know about the dangers of being alone, no rider would travel alone at night." Bukhari transmitted it.
Source: sunnah.com
Other translations
Arabic
وَعَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «لَوْ يَعْلَمُ النَّاسُ مَا فِي الْوَحْدَةِ مَا أَعْلَمُ مَا سَارَ رَاكِبٌ بِلَيْلٍ وَحْدَهُ» . رَوَاهُ الْبُخَارِيُّ
sunnah.com