Musnad Ahmad 175:30

Muhammad ibn Sabiq narrated to us, he said: Ibrahim ibn Tahman informed us, from Abu al-Zubayr, from Ibn Ka'b ibn Malik, from his father Ka'b ibn Malik, that he narrated to him: That the Messenger of Allah (peace and blessings of Allah be upon him) sent him and Aws ibn al-Hadathan during the Days of Tashriq, and they proclaimed: "That none shall enter Paradise except a believer, and the Days of Tashriq are days of eating and drinking."