Al-Kāfi - The Book of Prayer

Chapter: Salah (Prayer) Is Made Obligatory (Chapters 3-15, practical rules about prayer are best expressed in the form of fatwa.) َّادٌ عَنْ حَرِيزٍ عَنْ زُرَارَةَ عَنْ أَبِي جَعْفَرٍ (عَلَيْهِ الْسَّلا٠) فِي قَوْلِ الله عَزَّ وَجَلَّ إِنَّ الصَّلاةَ كانَتْ عَلَى الْ٠4.

Hammad has narrated from Hariz from Zurarah from who has said the following: “About the words of Allah, most Majestic, most Glorious, ‘Salah (prayer) in Mawqut (with certain timing) form was written on believers’ abu Ja‘far (a.s.), has said, ‘it means obligatory.’” صحيح - Allamah Baqir al-Majlisi (Mirʾāt al-ʿUqūl fī Sharḥ Akhbār Āl al-Rasūl (15/24))