Musannaf Ibn Abi Shayba 36:101

Waki’ narrated to us, from Qurrah ibn Khalid al-Sadusi, from Yazid ibn Abdullah ibn al-Shikhkhir, who said: We were sitting in this al-Mirbad in Basra, and a Bedouin came with a piece of leather or a piece of a leather bag. He said: "This is a document the Prophet, may Allah bless him and grant him peace, wrote for me." He said: So I took it and read it to the people, and in it was: "In the name of Allah, the Most Gracious, the Most Merciful. From Muhammad, the Messenger of Allah, may Allah bless him and grant him peace, to the Banu Zuhayr ibn Uqaysh: If you establish prayer, give zakat, and give from the spoils the fifth, the share of the Prophet, and the *safiy* (the choice portion), then you are secure with the security of Allah and the security of His Messenger." He said: I did not hear the Messenger of Allah, may Allah bless him and grant him peace, say anything [else]. He said: I heard him say: "Fasting the month of patience (Ramadan) and three days of every month removes the malice of the chest."