(39) بَابُ: {وَاذْكُرْ عَبْدَنَا دَاوُدَ ذَا الأَيْدِ إِنَّهُ أَوَّابٌ} إِلَى قَوْلِهِ: {وَفَصْلَ الْخِطَابِ}
Narrated Ibn `Abbas:
The prostration in Sura-Sa`d is not amongst the compulsory prostrations, though I saw the Prophet (ﷺ) prostrating on reciting it.
Reference: Sahih al-Bukhari 3422
In-book reference: Book 60, Hadith 94
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 4, Book 55, Hadith 633