The Prophet ﷺ came to Medina and the people used to pay in advance the prices of fruits to be delivered within two to three years. The Prophet ﷺ said (to them), "Buy fruits by paying their prices in advance on condition that the fruits are to be delivered to you according to a fixed specified measure within a fixed specified period." Ibn Najih said, " ... by specified measure and specified weight."  

قَدِمَ النَّبِيُّ ﷺ الْمَدِينَةَ وَهُمْ يُسْلِفُونَ فِي الثِّمَارِ السَّنَتَيْنِ وَالثَّلاَثَ فَقَالَ أَسْلِفُوا فِي الثِّمَارِ فِي كَيْلٍ مَعْلُومٍ إِلَى أَجَلٍ مَعْلُومٍ وَقَالَ عَبْدُ اللَّهِ بْنُ الْوَلِيدِ حَدَّثَنَا سُفْيَانُ حَدَّثَنَا ابْنُ أَبِي نَجِيحٍ وَقَالَ فِي كَيْلٍ مَعْلُومٍ وَوَزْنٍ مَعْلُومٍ  

Abu Burda and ʿAbdullah bin Shaddad sent me to ʿAbdur Rahman bin Abza and ʿAbdullah bin Abi ʿAufa to ask them about the Salaf (Salam). They said, "We used to get war booty while we were with Messenger of Allah ﷺ and when the peasants of Sham came to us we used to pay them in advance for wheat, barley, and oil to be delivered within a fixed period." I asked them, "Did the peasants own standing crops or not?" They replied, "We never asked them about it."  

عَنِ السَّلَفِ فَقَالاَ كُنَّا نُصِيبُ الْمَغَانِمَ مَعَ رَسُولِ اللَّهِ ﷺ فَكَانَ يَأْتِينَا أَنْبَاطٌ مِنْ أَنْبَاطِ الشَّأْمِ فَنُسْلِفُهُمْ فِي الْحِنْطَةِ وَالشَّعِيرِ وَالزَّبِيبِ إِلَى أَجَلٍ مُسَمًّى قَالَ قُلْتُ أَكَانَ لَهُمْ زَرْعٌ أَوْ لَمْ يَكُنْ لَهُمْ زَرْعٌ قَالاَ مَا كُنَّا نَسْأَلُهُمْ عَنْ ذَلِكَ