Chapter on the Manner of Prayer, Explanation of the Fifty-One Rak‘ahs; The Order, Recitation, Tasbih in Bowing and Prostration, Qunut, and What is Obligatory and Recommended Therein
Chapter on the Manner of Prayer, Explanation of the Fifty-One Rak‘ahs; The Order, Recitation, Tasbih in Bowing and Prostration, Qunut, and What is Obligatory and Recommended Therein
فمحمول على من كان في صلاة النافلة وقد قرأ من السورة الاخرى بعضها ويريد أن يقرأ باقيها فحينئذ لا يقرأ بسم الله الرحمن الرحيم والذي يبين ذلك ما رواه
So this is to be interpreted as referring to someone who is in a ‘nafila’ (supererogatory) prayer and has already recited part of another Surah and intends to continue the rest of it, in that case, he does not recite ‘Bismillah Hir Rahman Nir Rahim’. What clarifies this is what has been narrated:
Commentary #3