Hadith: The Messenger of Allah (may Allah's peace and blessings be upon him) granted concession to the owner of Al-‘Ariyyah (a dates palm) to sell its unpicked fruits for dry dates by estimation

عن زيد بن ثابت رضي الله عنه : «أن رسول الله صلى الله عليه وسلم رخص لصاحب العَرِيَّةِ: أن يبيعها بِخَرْصِهَا». ولمسلم: «بخرصها تمرا، يأكلونها رُطَبَاً».
[صحيح] - [متفق عليه]

Zayd ibn Thābit (may Allah be pleased with him) reported the Messenger of Allah (may Allah's peace and blessings be upon him) granted concession to the owner of Al-‘Ariyyah (a dates palm) to sell its unpicked fruits for dry dates by estimation. Another narration by Imām Muslim reads: "...for dry dates by estimation and the new owners might eat their dates fresh."
[Authentic hadith] - [Narrated by Bukhari & Muslim]

Explanation

Selling dates on the trees for dry dates is forbidden. This transaction is called Al-Muzābanah that is prohibited because the weight of the dates, which is required to be equal in goods subject to rulings of usury, is not known. Currencies like dinars and dirhams were scarce in the past. Sometimes seasons of the fresh ripe dates would arrive, and people in Madīnah need to eat them; yet, they did not have the money to purchase them. Therefore, it was made permissible for them to purchase some ripe dates to eat in exchange for dry dates by estimation, taking into consideration that they should be approximately equal in amount were the dates on the trees to become dry. This kind of Al-‘Ariyyah transaction was an exception to the rule of prohibition applicable to Al-Muzābanah.