“The Messenger of Allah—may Allah’s peace and blessings be upon him—would not abandon fasting the White Days, whether while traveling or while resident.”

Narrated by al-Nasāʾī (no. 2345), al-Ṭabarānī in al-Kabīr (no. 12320), and al-Ḍiyāʾ in al-Mukhtārah (no. 100), with the wording being theirs, from the ḥadīth of Ibn ʿAbbās (may Allah be pleased with them both).
Authenticated in Ṣaḥīḥ al-Jāmiʿ (no. 4848) and Silsilat al-Aḥādīth al-Ṣaḥīḥah (no. 580).

Brief Explanation of the Hadith

This ḥadīth indicates the Prophet’s—may Allah’s peace and blessings be upon him—strong consistency in acts of obedience and his keen concern for maintaining regularity in voluntary acts of worship. Among these is fasting the White Days, whether while resident or traveling, as reported by Ibn ʿAbbās—may Allah be pleased with them both.
The meaning of his statement, “he would not abandon…,” is that he did not leave off fasting them whether while resident or traveling; rather, he consistently observed them both at home and on journeys, due to the great virtue found in these days, for fasting three days of every month is equivalent to fasting an entire lifetime.
The White Days are the thirteenth, fourteenth, and fifteenth of every lunar month. They are so named due to the illumination of their nights by the moon, making fasting them an act of gratitude to Allah, the Exalted. It has also been said that when light encompasses their nights, it is fitting that worship encompass their days.
In the ḥadīth there is an indication that voluntary fasting is not restricted to residence; rather, it is legislated even during travel, so long as no excessive hardship befalls the one who is fasting. This does not contradict his statement—may Allah’s peace and blessings be upon him— “It is not from righteousness to fast while traveling,” for it is to be understood as referring to one for whom fasting entails hardship or leads to neglect of rights and obligations. As for one who is able to fast without harm or undue difficulty, his fasting is legislated—and may even be virtuous—based on the evidence of the Sunnah.
In his consistent observance—may Allah’s peace and blessings be upon him—there is a practical form of instruction for the Ummah and a clarification of the great virtue of small deeds when their performer maintains them regularly. For the Sacred Law has equated fasting three days of every month with fasting an entire lifetime, because a good deed is rewarded tenfold: fasting one day is equivalent to fasting ten days, and fasting three days is equivalent to fasting thirty days. Thus, whoever consistently fasts them every month is as though he has fasted a lifetime; whereas whoever fasts them in some months receives the reward of fasting thirty days for each month in which he fasted.
In the ḥadīth there is an exhortation to maintain consistency in acts of obedience, and a clarification that voluntary acts of worship are not to be abandoned during travel so long as they do not involve hardship, and that from the guidance of the Prophet—may Allah’s peace and blessings be upon him—is steadfastness upon righteous deeds and persistence in them.