Abu Dawud Book 4, Hadith Number 1854.

Narated By Ka’b ibn Ujrah : The Apostle of Allah (PBUH) came upon him (during their stay) at al-Hudaybiyyah. He then narrated the rest of the tradition. This version adds: “He asked: Do you have a sacrificial animal? He replied: No. He then said: Fast three days or give three sa’s of dates to six poor people, giving one sa’ to every two persons.”