Musnad Ahmad 1018:9

Waki' narrated to us, Qurra ibn Khalid narrated to me, from Yazid ibn Abdullah ibn al-Shikhkhir, from the Bedouin, who said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "Fasting the month of patience [Ramadan] and three days of every month removes the rancor of the chest."