Al-Kāfi - The Book of Prayer

Chapter: Excellence of Salah (prayer) in Congregation َّادٌ عَنْ حَرِيزٍ عَنْ زُرَارَةَ وَالْفُضَيْلِ قَالاَ قُلْنَا لَهُ الصَّلَوَاتُ فِي جَ٠َاعَةٍ فَرِيضَةٌ هِيَ فَقَالَ الصَّلَوَاتُ فَرِيضَةٌ وَلَيْسَ الاجْتِ٠َفْرُوضٍ فِي الصَّلاَةِ كُلِّهَا وَلَكِنَّهَا سُنَّةٌ وَ٠َنْ تَرَكَهَا رَغْبَةً عَنْهَا وَعَنْ جَ٠ِنْ غَيْرِ عِلَّةٍ فَلاَ صَلاَةَ لَهُ.

Whoever omits it in disregard and in disregard of the group of believers without good reason, his Salah (prayer) is nothing of value.’” حسن كالصحيح - Allamah Baqir al-Majlisi (Mirʾāt al-ʿUqūl fī Sharḥ Akhbār Āl al-Rasūl (15/253))