Narrated [Abu Hurairah (RA)]:

Allah's Messenger (ﷺ) said: "If you see someone buying or selling inside the mosque, say: 'May Allah not make your trading profitable!'" [Reported by an-Nasa'i and at-Tirmidhi and the latter graded it Hasan (good)].

وَعَنْهُ : أَنَّ رَسُولَ اَللَّهِ ‏- صلى الله عليه وسلم ‏-{ إِذَا رَأَيْتُمْ مَنْ يَبِيعُ , أَوْ يَبْتَاعُ فِي اَلْمَسْجِدِ , فَقُولُوا : لَا أَرْبَحَ اَللَّهُ تِجَارَتَكَ } رَوَاهُ النَّسَائِيُّ , وَاَلتِّرْمِذِيُّ وَحَسَّنَهُ .‏ [1]‏