وَلَا يَجُوزُ أَنْ يَبِيعَ ثَمَرَةً وَيَسْتَثْنِيَ مِنْهَا أَرْطَالًا مَعْلُومَةً
Translation: It is not permitted to sell fruit while reserving a specified number of ratls from it.
Yastathni means excluding something from the subject of sale.
Artalan maʿlumah means a known number of ratls, a historical unit of weight.
This ruling concerns fruit still attached and not separately weighed or apportioned. The unseparated remainder becomes insufficiently determined, creating problematic uncertainty in what the buyer receives.