The Time for Night Prayer
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 66
وَ رُوِيَ عَنْ مُعَاوِيَةَ بْنِ وَهْبٍ أَنَّهُ قَالَ: قُلْتُ لَهُ إِنَّ رَجُلاً مِنْ مَوَالِيكَ مِنْ صُلَحَائِهِمْ شَكَا إِلَيَّ مَا يَلْقَى مِنَ اَلنَّوْمِ وَقَالَ لِي إِنِّي أُرِيدُ اَلْقِيَامَ لِصَلاَةِ اَللَّيْلِ فَيَغْلِبُنِي اَلنَّوْمُ حَتَّى أُصْبِحَ فَرُبَّمَا قَضَيْتُ صَلاَتِي اَلشَّهْرَ اَلْمُتَتَابِعَ أَوِ اَلشَّهْرَيْنِ أَصْبِرُ عَلَى ثِقَلِهِ فَقَالَ «قُرَّةُ عَيْنٍ وَ اَللَّهِ قُرَّةُ عَيْنٍ وَ اَللَّهِ وَ لَمْ يُرَخِّصْ فِي اَلْوَتْرِ أَوَّلَ اَللَّيْلِ» فَقَالَ «اَلْقَضَاءُ بِالنَّهَارِ أَفْضَلُ.
It is reported from Mu'awiyah ibn Wahb that He said: "I said to him (Abu Abdullah عليه السلام): 'One of your followers, who is among your righteous adherents, complained to me about the difficulty he experiences with sleep. He said to me: ‘I wish to rise for the night prayer (salat al-layl), but sleep overcomes me until I wake up in the morning. Sometimes I make up my prayer continuously for a month or two and endure the difficulty.’ Imam عليه السلام said: 'By Allah سبحانه وتعالى, it is a source of delight, by Allah سبحانه وتعالى, it is a source of delight!' But he did not permit performing the Witr (single unit of the night prayer) at the beginning of the night. Imam عليه السلام said: 'Making it up during the day is better.'"
- Ṣaḥīḥ al-Faqīh, p. 69