"The Messenger of Allah forbade selling a heap of dried dates whose volume is unknown for known volume of dried dates," (Using translation from Nasāʾī 4547)  

أَنَّهُ سَمِعَ جَابِرَ بْنَ عَبْدِ اللهِ يَقُولُ نَهَى رَسُولُ اللهِ ﷺ عَنْ بَيْعِ الصُّبْرَةِ مِنَ التَّمْرِ لَا يُعْلَمُ مَكِيلَتُهَا بِالْكَيْلِ الْمُسَمَّى مِنَ التَّمْرِ