"The Messenger of Allah ﷺ prohibited Al-Muhaqalah, Al-Muzabanah, Al-Mukhabarah, and making an exception (in a sale) unless it is made known."  

أَنَّ رَسُولَ اللَّهِ ﷺ نَهَى عَنِ الْمُحَاقَلَةِ وَالْمُزَابَنَةِ وَالْمُخَابَرَةِ وَالثُّنْيَا إِلاَّ أَنْ تُعْلَمَ