Sunan an-Nasa'i 760
سنن النسائي#760Sahihأَخْبَرَنَا عَلِيُّ بْنُ حُجْرٍ، قَالَ حَدَّثَنَا الْوَلِيدُ، عَنِ ابْنِ جَابِرٍ، عَنْ بُسْرِ بْنِ عُبَيْدِ اللَّهِ، عَنْ وَاثِلَةَ بْنِ الأَسْقَعِ، عَنْ أَبِي مَرْثَدٍ الْغَنَوِيِّ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " لاَ تُصَلُّوا إِلَى الْقُبُورِ وَلاَ تَجْلِسُوا عَلَيْهَا " .
It was narrated that Abu Marthad al Ghanawi said:"The Messenger of Allah(ﷺ)said: 'Do not pray toward graves and do not sit on them
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiSahih Muslim
In-book reference: 9:19