Sunan Ibn Majah, Volume 5, Book 33, Hadith 3768 (DarusSalam) ⓘ
It was narrated from Ibn 'Umar that the Messenger of Allah said: "If anyone of you knew what is wrong with being alone, no one would travel at night by himself."
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا وَكِيعٌ، عَنْ عَاصِمِ بْنِ مُحَمَّدٍ، عَنْ أَبِيهِ، عَنِ ابْنِ عُمَرَ، قَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ " لَوْ يَعْلَمُ أَحَدُكُمْ مَا فِي الْوَحْدَةِ مَا سَارَ أَحَدٌ بِلَيْلٍ وَحْدَهُ " .
also referenced under: Hadith 3768 (Reference) & Book 33, Hadith 113 (In-Book)