Sayyidina Ibn Abbas (RA) reported that when Allah’s Messenger (SAW) came to Madinah, the Madinans used to pay in advance for dates. So he instructed, “If anne receives advance payment then it is necessary to specify the weight or measure and the time of delivery.”
[Bukhari 2239, Nisai 1604, Abu Dawud 3463, Ibn e Majah 2280, Ahmed 2458]