Bukhari

Hadith Commentary:
Qastallani (rahimahullah) said that perhaps the Prophet (sallallahu alayhi wa sallam) initially gave this ruling as a matter of advice and consultation, as indicated by the words "kalmashurah yashiru biha" (as a consultation he advised with it).
Then, after that, he absolutely prohibited it.
As is found in the hadith of Ibn Umar (radi Allahu anhu), and the evidence for this is that Zayd ibn Thabit (radi Allahu anhu) himself, who is the narrator of this hadith, would not sell his fruit before it had ripened.
"Thurayya" is a star that rises at the time of true dawn at the beginning of summer.
In the land of Hijaz, there is intense heat at that time, and the fruits ripen.

Hadith Commentary:
(1)
There is considerable disagreement regarding the buying and selling of fruits before their ripeness becomes apparent and before they become usable. Due to the strength of this disagreement, Imam Bukhari rahimahullah did not make any definitive or categorical ruling. According to Ibn Abi Ya’la and Imam Thawri rahimahullah, such a transaction is absolutely impermissible, whereas some scholars declare it absolutely permissible. The Hanafi scholars consider it permissible. According to them, the meaning of the hadith is that buying and selling fruits before their existence is prohibited.

(2)
The meaning of the ripeness becoming apparent is that the sourness and hardness of the fruits disappear and sweetness and softness appear in them, i.e., they become usable. At the rising of the Thurayya star, the fruits would become usable, which is why Zayd ibn Thabit radi Allahu anhu used to sell his fruits after the rising of Thurayya. Due to the frequency of disputes, the Messenger of Allah sallallahu alayhi wa sallam said: “Do not sell the fruit until it becomes usable, so that there is no dispute or the like.” It should be noted that “damān” is a disease of fruits due to which the fruits would turn black. In one narration, instead of “disease” (marad), the word “marād” is used. “Marād” is a calamity from the sky, due to which the fruits would be destroyed. “Qishām” is also a disease, due to which the fruit would fall before turning yellow. When the fruits are safe from such calamities and diseases, then their buying and selling is permitted. (Fath al-Bari: 4/499)