Mishkat al-Masabih 11 Business Transactions كتاب البيوع 89

وَعَنْ أَبِي هُرَيْرَةَ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: «لَا يَسُمِ الرَّجُلُ على سَوْمِ أخيهِ الْمُسلم» . رَوَاهُ مُسلم

Abu Huraira reported God’s Messenger as saying, “A man must not offer a price above that offered by his brother Muslim.” Muslim transmitted it.