On the authority of ʿAbd Allāh ibn ʿAmr, who said: The Messenger of Allah, peace and blessings be upon him, said: "The most excellent fast is the fast of my brother David. He used to fast one day and break his fast one day, and he would not flee when he met [the enemy]."(1)

This is a ḥasan ṣaḥīḥ ḥadīth.

Abū al-ʿAbbās: he is the blind poet, and his name is al-Sāʾib ibn Farrūkh.

Some of the people of knowledge said: The most excellent fasting is that you fast one day and break your fast one day. And it is said: This is the most rigorous form of fasting.

58 - Chapter: What has been reported concerning the disapproval of fasting on the Day of Fiṭr and the Day of Naḥr

781 - Qutaybah narrated to us, saying: ʿAbd al-ʿAzīz ibn Muḥammad narrated to us, from ʿAmr ibn Yaḥyā, from his father, from Abū Saʿīd al-Khudrī, who said: The Messenger of Allah, peace and blessings be upon him, forbade two fasts: the Day of al-Aḍḥā and the Day of al-Fiṭr(2)(3).

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(1) A ṣaḥīḥ ḥadīth. It was also recorded by al-Bukhārī (1976), Muslim (1159), Ibn Mājah (1712), al-Nasāʾī 4/209, 210, 211, and 213, and it is in al-Musnad (6534) and Ṣaḥīḥ Ibn Ḥibbān (352).
(2) A ṣaḥīḥ ḥadīth. It was also recorded by al-Bukhārī (1991), Muslim (827) (141), 2/800, and Abū Dāwūd (2417), and it is in al-Musnad (11910).
(3) This ḥadīth and its commentary were delayed in the printed edition, and in the copy upon which al-Ḥāfiẓ al-ʿIrāqī commented, as well as Ibn al-ʿArabī, until after the following ḥadīth, but it appears here in all of our manuscript copies.