Silsilat al-Ahadith al-Sahihah

Sayyiduna Abu Hurairah (may Allah be pleased with him) says: A Bedouin brought a roasted rabbit along with its gravy to the Messenger of Allah (peace and blessings of Allah be upon him) and placed it before him. The Prophet (peace be upon him) paused and did not eat, and the noble Companions also paused and did not eat, and the Bedouin himself also paused. The Messenger of Allah (peace be upon him) said: Why are you not eating? He said: I fast three days every month. The Prophet (peace be upon him) said: "If you are to fast, then fast on the bright days (i.e., the days of the full moon)." By this, the Prophet (peace be upon him) meant the Ayyam al-Beedh (the white days).