Musnad Abu Ya'la al-Mawsili 129:27

'Abd al-A'la al-Narsi narrated to us, Hammad narrated to us, Humayd narrated to us, from Anas, that the Messenger of Allah (may Allah bless him and grant him peace) forbade the selling of fruit until it shows color, and the selling of grapes until they turn black, and the selling of grain until it hardens.