Muwatta Imam Malik Book of Business Transactions, Hadith 13
Yahya related to me from Malik from Abu'z-Zinad from Kharija ibn Zayd ibn Thabit that Zayd ibn Thabit did not sell fruit until the Pleiades were visible, at the end of May.
Malik said, "The way of doing things among us about selling melons, cucumbers, water- melons, and carrots is that it is halal to sell them when it is clear that they have begun to ripen. Then the buyer has what grows until the season is over. There is no specific timing laid down for that because the time is well known with people, and it may happen that the crop will be affected by blight and put a premature end to the season. If blight strikes and a third or more of the crop is damaged, an allowance for that is deducted from the price of purchase."
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ أَبِي الزِّنَادِ، عَنْ خَارِجَةَ بْنِ زَيْدِ بْنِ ثَابِتٍ، عَنْ زَيْدِ بْنِ ثَابِتٍ، أَنَّهُ كَانَ لاَ يَبِيعُ ثِمَارَهُ حَتَّى تَطْلُعَ الثُّرَيَّا .