Al-Kāfi - The Book of Prayer

Chapter: Rules about the Very Old or One with an Illness 11ـ عَلِيٌّ عَنْ أَبِيهِ عَنِ ابْنِ ٠َحْبُوبٍ عَنْ أَبِي حَ٠ْزَةَ عَنْ أَبِي جَعْفَرٍ (عَلَيْهِ الْسَّلا٠) فِي قَوْلِ الله عَزَّ وَجَلَّ الَّذِينَ يَذْكُرُونَ الله قِيا٠اً وَقُعُوداً وَعَلى‏ جُنُوبِهِ٠ْ قَالَ الصَّحِيحُ يُصَلِّي قَائِ٠اً وَقُعُوداً الْ٠َرِيضُ يُصَلِّي جَالِساً وَعَلى‏ جُنُوبِهِ٠ْ الَّذِي يَكُونُ أَضْعَفَ ٠َرِيضِ الَّذِي يُصَلِّي جَالِساً.

One suffering from an illness performs Salah (prayer) sitting, and ‘on their sides’ is for one who is weaker than a patient who performs Salah (prayer) in a sitting position.’” حسن - Allamah Baqir al-Majlisi (Mirʾāt al-ʿUqūl fī Sharḥ Akhbār Āl al-Rasūl (5/335))