Anas bin Sirin أنس بن سيرين الأنصاري · The Book of Fasting

"You should fast the thirteenth, fourteenth and fifteenth." (Hasan) Abu 'Abdur-Rahman (An-Nasai) said: This is a mistake, it is not a narration of Bayan; perhaps Sufyan said: "It was narrated to us by two (Ithnan)" and the 'Alif was dropped so it became Bayan.

That the Prophet commanded a man to fast on the thirteenth, fourteenth and fifteenth.

"Ubayy said: 'A Bedouin came to the Messenger of Allah, and he had a rabbit that he had grilled and some bread. He placed it before the Prophet then he said: "I found it bleeding." The Messenger of Allah said to his Companions: "It doesn't matter; eat." And he said to the Bedouin: "Eat," He said: "I am fasting." He said: "If you want to fast then you should fast the shining days of Al-Bid: The thirteenth, fourteenth and fifteenth."