Bulugh al-Maram 2 The Book of Prayer كتاب الصلاة 238

وَعَنْ اِبْنِ عَبَّاسٍ -رَضِيَ اَللَّهُ عَنْهُمَا- قَالَ : { ( ص ) لَيْسَتْ مِنْ عَزَائِمِ اَلسُّجُودِ , وَقَدْ رَأَيْتُ رَسُولَ اَللَّهِ – صلى الله عليه وسلم -يَسْجُدُ فِيهَا } رَوَاهُ اَلْبُخَارِيُّ . 1 1 – صحيح . رواه البخاري ( 1069 ) .

Narrated Ibn ‘Abbas (RA): A prostration while reciting Surat Sad (Surah 38) is not one of the ‘Azaa’im (those which are always required), but I have seen Allah’s Messenger (صلى الله عليه وسلم) prostrating while reciting it. [Reported by al-Bukhari].