Sahih Muslim Book - 21, Hadith - 3864

وَحَدَّثَنِى عَلِىُّ بْنُ حُجْرٍ السَّعْدِىُّ وَزُهَيْرُ بْنُ حَرْبٍ قَالاَ حَدَّثَنَا إِسْمَاعِيلُ عَنْ أَيُّوبَ عَنْ نَافِعٍ عَنِ ابْنِ عُمَرَ أَنَّ رَسُولَ اللَّهِ -صلى الله عليه وسلم- نَهَى عَنْ بَيْعِ النَّخْلِ حَتَّى يَزْهُوَ وَعَنِ السُّنْبُلِ حَتَّى يَبْيَضَّ وَيَأْمَنَ الْعَاهَةَ نَهَى الْبَائِعَ وَالْمُشْتَرِىَ.

It was narrated from Ibn 'Umar that the Messenger of Allah (s.a.w) forbade selling the fruit of date palms until it began to develop color (turn yellow or red) and ears (of grain) until they turned white (having developed) and were free of blight. He forbade that to the seller and the buyer.