It was narrated that Ibn al-Hawtakiyyah said: Some food was brought to 'Umar bin al-Khattab and he called a man to join him, but he said, I am fasting. ['Umar] said: What fast are you observing? Were it not for fear of adding or subtracting something, I would have narrated to you a hadeeth, from the Prophet (ﷺ), when the Bedouin brought him a rabbit; rather send for 'Ammar. When 'Ammar came, he said: Were you there on the day when the Bedouin brought the rabbit to the Messenger of Allah (ﷺ)? ('Ammar) said: Yes. ('Umar] said: I saw blood on it, but he (the Prophet (ﷺ) said: `Eat it.` (The Bedouin) said: I am fasting. (The Prophet (ﷺ) said: `What fast are you observing?” He said: The beginning and end of the month. He said: “If you want to fast, then fast the thirteenth, fourteenth and fifteenth (of the month).`
Musnad Ahmad, 210[Hasan because of corroborating evidence (Darussalam)
