وبيع المزابنة - وهو بيع الثمر على رؤوس النخل بخرصه تمرا - ولا يجوز البيع بإلقاء الحجر والملامسة
Translation: Muzabana—selling fruit on trees against estimated quantities of dried dates—and sale concluded by throwing a stone or mere touching are disallowed.
Muzabana exchanges fruit on trees for dried dates by estimated yield, with the equivalence unknown.
In bay‘ al-hasah, throwing a stone determined a transaction or its subject. In mulamasah, touching an object could be made to finalize the sale without proper identification.
The broader learning point is clear specification of goods, price, and informed agreement.