Narrated Abu Hurairah (RA):

Allah's Messenger (ﷺ) said: "Whenever you recite Surat Al-Fatiha, recite Bismillahir-Rahmanir-Rahim, for it is one of its Ayat (Verses)." [Reported by ad-Daraqutni who verified it as Mawquf - the saying of Abu Hurairah (RA)].

وَعَنْ أَبِي هُرَيْرَةَ ‏- رضى الله عنه ‏- قَالَ : قَالَ رَسُولُ اَللَّهِ ‏- صلى الله عليه وسلم ‏-{ إِذَا قَرَأْتُمْ اَلْفَاتِحَةِ فَاقْرَءُوا : ( بِسْمِ اَللَّهِ اَلرَّحْمَنِ اَلرَّحِيمِ )‏ , فَإِنَّهَا إِحْدَى آيَاتِهَا } رَوَاهُ اَلدَّارَقُطْنِيُّ , وَصَوَّبَ وَقْفَهُ .‏ [1]‏