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

And al-Husayn ibn Sa‘id narrated from al-Qarawi from Aban from ‘Umar ibn Yazid who said: I said to Abu Abdillah عليه السلام: “May I recite two Surahs in one rak‘ah?” Imam عليه السلام said: “Yes.” I asked: “Is it not said that each Surah should be given its due in bowing and prostration?” Imam عليه السلام said: “That applies in the obligatory prayer, but as for the supererogatory prayer, there is no harm in it.”