Ibn Hu Takiyah says that food was presented to Sayyiduna Umar (may Allah be pleased with him). He invited a man to eat, but he said: I am fasting. He (Umar) asked: On which days do you fast? If there was no fear of error, I would have told you a hadith of the Noble Prophet (peace and blessings be upon him), according to which a Bedouin once brought a rabbit to him. However, you should call Sayyiduna Ammar (may Allah be pleased with him). When he came, Sayyiduna Umar (may Allah be pleased with him) asked him: Were you present on the day when a Bedouin brought a rabbit to the service of the Noble Prophet (peace and blessings be upon him)? He replied: Yes. The Bedouin said: I saw that it bleeds. The Prophet (peace and blessings be upon him) said: You may eat it. The Bedouin said: I am fasting. The Prophet (peace and blessings be upon him) asked him: On which days of the month do you fast? He said: At the beginning and end of the month. The Prophet (peace and blessings be upon him) said: If you wish to fast, then fast on the 13th, 14th, and 15th of the lunar month.