Yazid bin Abdullah bin al-Shikhkhir (may Allah have mercy on him) says: We were sitting in al-Mirbad, and I think I was the youngest of the people. A man from the desert came to us, and when we saw him we said: "It seems this man is not from this town." He said: "Yes." He had with him a piece of leather with writing on it, and he said: "This was written for me by the Messenger of Allah (peace and blessings be upon him)." In it was written:
"Bismillah al-Rahman al-Rahim (In the name of Allah, the Most Gracious, the Most Merciful). From Muhammad the Prophet (peace and blessings be upon him) to Banu Zuhayr bin Uqaysh, a clan of Ukl: If you establish the prayer, pay the zakah, separate yourselves from the polytheists, and give the khumus (one-fifth) from the spoils, then the share of the Prophet (peace and blessings be upon him) and al-safi (the chosen portion), then you are safe under the protection of Allah and the protection of His Messenger (peace and blessings be upon him)." They said: "Come, tell us, may Allah make you righteous, what you heard from the Messenger of Allah (peace and blessings be upon him)." He said: I heard the Messenger of Allah (peace and blessings be upon him) say: "Fasting the month of patience and three days of every month removes much of the rancour of the chest." Qurrah says: I said to him: "Wagharu al-sadr (the heat of the chest)?" He said: "Waharu al-sadr (the rancour of the chest)." The people said: "Did you really hear this from the Messenger of Allah (peace and blessings be upon him)?" He reached for his document, took it and went off quickly, then said: "Indeed, I see that you fear that I am lying about the Messenger of Allah (peace and blessings be upon him). By Allah! I will not narrate any hadith to you today."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الفيء والغنيمة / 12749