Al-Kāfi - The Book of Prayer

Chapter: Recitations in Salah (prayer) َّدُ بْنُ يَحْيَى عَنْ ٠َّدِ بْنِ الْحُسَيْنِ عَنْ صَفْوَانَ عَنِ ابْنِ بُكَيْرٍ عَنْ زُرَارَةَ عَنْ أَبِي جَعْفَرٍ (عَلَيْهِ الْسَّلا٠َا يُكْرَهُ أَنْ يُجْ٠َعَ بَيْنَ السُّورَتَيْنِ فِي الْفَرِيضَةِ فَأَ٠َّا النَّافِلَةُ فَلاَ بَأْسَ. 10.

Muhammad ibn Yahya has narrated from Muhammad ibn al-Husayn from Safwan from ibn Bukayr from Zurarah who has said the following: “Abu Ja’far (a.s.), has said, ‘It is undesirable to recite two Surah (chapters) together in an obligatory Salah (prayer) but in an optional one it is not harmful.’” (Ahadith 7-11 are best explained in the form of fatwa.) وثق - Allamah Baqir al-Majlisi (Mirʾāt al-ʿUqūl fī Sharḥ Akhbār Āl al-Rasūl (15/109))