إِنْ كَانَ يَوْمَ ابْتَاعَهُ سَاعَرَهُ أَنَّ لَهُ كَذَا وَ كَذَا فَإِنَّمَا لَهُ سِعْرُهُ وَ إِنْ كَانَ إِنَّمَا أَخَذَ بَعْضاً وَ تَرَكَ بَعْضاً وَ لَمْ يُسَمِّ سِعْراً فَإِنَّمَا لَهُ سِعْرُ يَوْمِهِ الَّذِي يَأْخُذُ فِيهِ مَا كَانَ.
“About the case of a man who buys food for a few dirham of which he takes one-half and leaves the other half. Thereafter he comes back when prices have risen or have fallen down, Abu ‘ Abd Allah (a.s.), has said, ‘If on the day of purchase he prices them and determines the amount then such price is what it is, but if h