Al-Kāfi - Volume 6 > The Undesirable Case of One’s Sleeping Alone and the Characteristics Prohibited because of its Frightfulness
Hadith #1

مُحَمَّدُ بْنُ يَحْيَى عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنِ ابْنِ فَضَّالٍ عَنِ ابْنِ الْقَدَّاحِ عَنْ أَبِيهِ قَالَ نَزَلْتُ عَلَى أَبِي جَعْفَرٍ ( عليه السلام ) فَقَالَ يَا مَيْمُونُ مَنْ يَرْقُدُ مَعَكَ بِاللَّيْلِ أَ مَعَكَ غُلَامٌ قُلْتُ لَا قَالَ فَلَا تَنَمْ وَحْدَكَ فَإِنَّ أَجْرَأَ مَا يَكُونُ الشَّيْطَانُ عَلَى الْإِنْسَانِ إِذَا كَانَ وَحْدَهُ .

1. Muhammad ibn Yahya has narrated from Ahmad ibn Muhammad from ibn Faddal from ibn al-Qaddah from his father who has said the following: “I once visited abu Ja‘far, ‘Alayhi al-Salam, and he asked saying, ‘O Maymun, who sleeps near you in the night, is there a slave with you?’ I replied, ‘No, no one sleeps near me.’ He (the Imam) said, ‘Do not sleep alone; Satan becomes more daring against man when he finds him alone.’”