It is narrated from Sayyiduna Zayd bin Thabit (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Nothing of the fruit is to be sold until its ripeness becomes evident, and its ripeness is that a red or yellow colour becomes apparent in it."
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 4809