رِيَاضُ الصَّالِحِينَ
Riyad as-Salihin 1580
The Book of the Prohibited actions
Prohibition of Deceiving others
وَعَنْهُ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ ، قَالَ: لَا تناجشوا ((مُتَّفَقٌ عَلَيْهِ)).
Abu Hurairah (May Allah be pleased with him) said: The Messenger of Allah (ﷺ) said, "Do not practise Najsh (to cheat)." [Muslim].
Riyad as-Salihin, 1580