It is narrated from Sayyiduna Jabir (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever sells (buys) fruit, then a calamity befalls that (fruit), he must never take the buyer's wealth. On what basis are you taking your Muslim brother's wealth?"
Hadith Referenceسنن دارمي / من كتاب البيوع / 2592
Hadith Gradingتحقیق (حسین سلیم أسد الدارانی):إسناده صحيح فقد صرح ابن جريج بالتحديث عند مسلم، [مكتبه الشامله نمبر: 2598]
It should be clear that by «جَائِحَةٌ» in the hadith is meant such a calamity that completely destroys the fruits, such as heavy rain, hailstorm, locust swarm, windstorm, hurricane, fire, etc.
Imam Ahmad rahimahullah and the Ahl al-Hadith have acted upon this hadith and have said that if a calamity befalls the fruits in such a way that all the fruits are destroyed, then the entire price will be returned from the seller (bā’iʿ) to the buyer (mushtarī), even if this calamity occurs after the buyer has taken possession.
The Hanafis and Shafi‘is say that if the buyer has taken possession of the fruits and then a calamity occurs, the loss will be borne by the buyer; in this case, the buyer must return the price to the seller because this sale was not valid.