"When the Prophet ﷺ came (to Al-Madinah), they used to pay in advance for dates, two or three years in advance. He said: 'Whoever pays in advance for dates, let him pay for a known amount or a known weight, to be delivered at a known time.’” (Using translation from Ibn Mājah 2280)
قَدِمَ النَّبِيُّ ﷺ الْمَدِينَةَ وَهُمْ يُسَلِّفُونَ فِي التَّمْرِالسَّنَتَيْنِ وَالثَّلاثَ فَقَالَ مَنْ سَلَّفَ فَلْيُسَلِّفْ فِي كَيْلٍ مَعْلُومٍ وَوَزْنٍ مَعْلُومٍ إِلَى أَجَلٍ مَعْلُومٍ