The Reward of the Night Prayer
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 65
وَ سَأَلَهُ عَبْدُ اَللَّهِ بْنُ سِنَانٍ: عَنْ قَوْلِ اَللَّهِ عَزَّ وَ جَلَّ: «سِيمٰاهُمْ فِي وُجُوهِهِمْ مِنْ أَثَرِ اَلسُّجُودِ» قَالَ «هُوَ اَلسَّهَرُ فِي اَلصَّلاَةِ.
Abdullah ibn Sinan asked him (Abu Abdullah عليه السلام) about the words of Allah سبحانه وتعالى, the Mighty and Majestic: "Their mark is on their faces from the trace of prostration" (Surah Al-Fath 48:29). Imam عليه السلام said: "It refers to staying awake for prayer."
- Ṣaḥīḥ al-Faqīh, p. 69