Musannaf Ibn Abi Shaybah

Hazrat Ibn Umar (may Allah be pleased with both of them) states that there is no harm in conducting a sale with advance payment (Salam) in wheat for a specified quantity and specified time, as long as the wheat is not still in the crop (i.e., Salam should be done only after the wheat has been harvested), and it is not permissible to conduct a sale with advance payment (Salam) in dates before they reach the stage of ripeness (Badu Salah).