Sahih Muslim Book 10, Hadith Number 3773.

Chapter : It is forbidden for a solvent to make delay in the payment of debt and the desirability of a reference, and it is excellent for the rich man to accept that when reference is made to him.

Anas (Allah be pleased with him) reported that Allah’s Apostle (may peace be upon him) forbade the sale of the fruit of date-palms until it becomes mellow. We (some of the other narrators in the chain of transmitters) said: What does the word” mellow” mean? He said: (There the fruit) turns red or yellow. Don’t you see if Allah had checked (the growth of) fruits; then what for the wealth of your brother would be permissible for you?