Sahih Bukhari, Chapter: Obligatory Charity Tax (Zakat)

Dates used to be brought to Allah's Apostle immediately after being plucked. Different persons would bring their dates till a big heap collected (in front of the Prophet). Once Al-Hasan and Al-Husain were playing with these dates. One of them took a date and put it in his mouth. Allah's Apostle looked at him and took it out from his mouth and said, "Don't you know that Muhammad's offspring do not eat what is given in charity?"