The Messenger of Allah ﷺ commanded us to fast three days each month, the white days, the thirteenth, the fourteenth, and the fifteenth.
أمرنا رسول الله ﷺ أن نصوم من الشهر ثلاثة أيام البيض: ثلاث عشرة، وأربع عشرة، وخمس عشرة.
Tirmidhi (761) and Nasai (2426) narrated it - and the wording is his - both through the route of Shuba, from Amash, who said, I heard Yahya bin Sam, from Musa bin Talha, who said, I heard Abu Dharr saying at Rabaza (then he related it). Tirmidhi said, "The hadith of Abu Dharr is a hasan hadith." Ibn Khuzayma graded it sahih (2128) through the route of Shuba, with his chain. Ibn Hibban narrated it (3566) through the route of Yahya Qattan, from Fitr, from Yahya bin Sam, with the same wording.Its chain is hasan. Musa bin Talha is the son of Ubaydullah Taymi, a trustworthy and eminent narrator. It is said that he was born during the time of the Prophet. Yahya bin Sam bin Musa Dabbi had a group of narrators report from him. Ibn Hibban mentioned him in Thiqat (7/606), and that is why Hafiz said in Taqrib, "Acceptable," meaning when corroborated.Two men corroborated him, as in the chain that follows, except that they inserted a man between Musa bin Talha and Abu Dharr, along with an addition of the story of the rabbit.Nasai (2428), Ahmad (21335), and Humaydi (136) all narrated it through the route of Sufyan bin Uyayna, who said, Muhammad bin Abdul-Rahman, freedman of the family of Talha, and Hakeem bin Jubayr narrated to us, both of whom heard it from Musa bin Talha, that he heard a man from his maternal uncles among Banu Tamim, called Ibn Hawtakiyya.He said, Umar bin Khattab said, "Which of you was present with us on the day of Qaha when a rabbit was brought to the Prophet ﷺ?" Abu Dharr said, "I was. A bedouin brought the Prophet ﷺ a rabbit and said, 'O Messenger of Allah, I saw it bleeding.'" He said, so the Prophet ﷺ refrained from it and did not eat, and he ordered his companions to eat, while the bedouin withdrew and did not partake. He said, "I am fasting." The Prophet ﷺ said, "What is your fast?" He said, "Three days every month." He said, "Then why not observe the brilliant white days, the thirteenth, the fourteenth, and the fifteenth?"The wording is Humaydi's, while Nasai and Ahmad, with this chain, confined themselves to mentioning the fasting only, without mentioning the story of the rabbit.Ibn Khuzayma graded it sahih (2127) through the route of Sufyan, from Muhammad bin Abdul-Rahman, freedman of the family of Talha, alone, from Musa bin Talha, with the same account, relating it in full similar to the hadith of Humaydi. He then said afterward, "I have covered this chapter in full in the book Kabir, and I have shown that Musa bin Talha heard from Abu Dharr the story of the fasting without the story of the rabbit, while he narrated both stories together from Ibn Hawtakiyya."Ibn Hawtakiyya is Yazid bin Hawtakiyya Tamimi, and Musa bin Talha alone narrated from him. Ibn Hajar said, "Acceptable." So the hadith is strengthened by this corroboration, and Tirmidhi graded it hasan while Ibn Khuzayma graded it sahih.Ibn Jareer Tabari narrated it in Tahzib Athar (949, Musnad of Umar) through another route, from Muhammad bin Abdul-Rahman, freedman of the family of Talha, from Musa bin Talha, from Ibn Hawtakiyya, who said, "I came to Umar bin Khattab while he was among a group of the companions of the Prophet ﷺ, and I asked him about fasting. He said, 'Which of you was with us when we were with the Prophet ﷺ at Qaha?' They said, 'We were, when the bedouin gave him a rabbit as a gift...'" and he related it in full. He graded its chain sahih.