Musannaf Ibn Abi Shayba 35:476

Waki’ narrated to us, from Shu’bah, from Muhammad ibn Ziyad, from Abu Hurairah, that the Messenger of Allah (may Allah bless him and grant him peace) saw al-Hasan ibn ‘Ali take a date from the charity (sadaqah) and chew it in his mouth. The Messenger of Allah (may Allah bless him and grant him peace) said, "Kakh, kakh! Indeed, charity is not lawful for us."