Abu Dawud

Benefits and Issues:
The thirteenth, fourteenth, and fifteenth dates are called the “Ayyam al-Beedh” (the days of the white nights) because, during these nights, the moon shines for almost the entire night.
The optimism (tafā’ul) in fasting on these days is that just as the darkness of these nights is replaced by brightness, likewise Allah, the Mighty and Majestic, will replace the darkness of the fasting person’s sins with whiteness and radiance.
And the command of the Prophet (sallallahu alayhi wa sallam) in this regard is in the sense of encouragement and motivation.

Benefit:
The aforementioned narration has been declared weak in its chain by our esteemed researcher. However, other hadiths of similar meaning are narrated from Abu Dharr al-Ghifari (radi Allahu anhu) and Ibn Abbas (radi Allahu anhuma), which Shaykh Abdul Qadir Arna’ut has graded as hasan in the footnotes of Jami’ al-Usul. See: (Jami’ al-Usul, Hadith: 4474)

The hadith of Abu Dharr (radi Allahu anhu) is found in Jami’ al-Tirmidhi and Sunan al-Nasa’i. See: (Jami’ al-Tirmidhi, Book of Fasting, Chapter: What Has Been Related About Fasting Three Days of Every Month, Hadith: 762; and Sunan al-Nasa’i, Book of Fasting, Chapter: Mention of the Difference Regarding Musa ibn Talhah in the End of Fasting Three Days of the Month, Hadith: 2426)

The hadith of Abdullah ibn Abbas (radi Allahu anhuma) is found in Sunan al-Nasa’i (Book of Fasting, Chapter: The Fasting of the Prophet sallallahu alayhi wa sallam, Hadith: 2347).

(1) All three narrations are reported by the same companion, however, there is a difference of opinion regarding the name of his father. Besides this, all three narrations are weak in their chains but correct in meaning. Shaykh al-Albani rahimahullah has graded these three narrations as hasan. See: (Irwa’ al-Ghalil: 4/101, 102. Hadith number: 947, Sahih Sunan al-Nasa’i: 2/170, 171, numbers: 2423, 2425, 2425)

(2) A command is not always for obligation; if there are contextual indicators, the command may also be for recommendation or permissibility. For example, in the Noble Qur’an it is stated: ﴿وَإِذَا حَلَلْتُمْ فَاصْطَادُوا﴾ () “When you have come out of ihram, then hunt.” ﴿فَإِذَا قُضِيَتِ الصَّلاةُ فَانْتَشِرُوا فِي الأرْضِ﴾ () “When the Friday prayer is finished, disperse in the land.” According to none of the scholars of knowledge are these two actions obligatory; if an ignorant person were to say so, that would be another matter.