Sayyiduna Zayd bin Thabit (may Allah be pleased with him) says that in the time of the Messenger of Allah (peace and blessings be upon him) people used to trade in fruits. When the people picked the fruit and the time for demanding payment came, the buyer would say that the fruit had been struck by "al-dumman" (that is, a disease before the fruit forms), that it had been struck by various kinds of diseases, "qusham" (a disease that strikes the date fruit before it ripens). They would make such excuses and arguments, so when the disputes became many, the Messenger of Allah (peace and blessings be upon him) said: "Do not sell fruits until the signs of their ripening become clear," as though he (peace and blessings be upon him) were advising them, because of their many disputes.
(b) Kharijah bin Zayd bin Thabit (may Allah have mercy on him) says that Zayd bin Thabit (may Allah be pleased with him) would not sell the fruits of his properties until the Pleiades rose, so that the red became distinct from the yellow. Abu al-Zinad (may Allah have mercy on him) mentioned the word "murad" instead of "maraq".
Al-Asma'i (may Allah have mercy on him) says: "Al-dumman" is the date palm splitting before (the fruit) appears from its spathe.
"Al-qusham": the date fruit falling before it ripens. "Murad": various kinds of diseases.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10605