Nasai

Hadith Commentary: Benefits and Issues: (1)
From all these narrations, it is established that performing prayer (salah) in a single garment is undoubtedly permissible, but a part of it should be on the shoulders. If, despite having the means and ability, one does not place the garment over the shoulders, then according to the majority of the imams, the prayer will be disliked (makruh). Imam Ahmad rahimahullah has an opinion that in such a case, the prayer will not be valid. If the garment is narrow and cannot be placed over the shoulders, then it should be used as a lower garment (izaar), even if the shoulders remain uncovered; this will not cause any deficiency in the prayer.

(2)
For prayer, only the covering of the private parts (satr) is obligatory; therefore, there is no harm in performing prayer in a single garment. However, when there are more garments available and a person generally keeps his head covered, then without any reason, praying with an uncovered head is not preferable. Al-Bukhari rahimahullah has transmitted the statement of Hasan al-Basri rahimahullah that (due to the heat) people (the noble Companions, radi Allahu anhum ajma‘in) used to prostrate on their turbans and caps (i.e., part of the turban and cap would be on the forehead), and their hands would be inside their sleeves. And Kulayb narrated from his maternal uncle: I visited the Messenger of Allah sallallahu alayhi wa sallam during winter, and he was praying in a burnous (a long hood or a garment that covers the head) and cloaks, and his hands were inside his cloaks. (Majma‘ al-Zawa’id) Ibn ‘Umar radi Allahu ta‘ala anhuma saw his slave praying with his head uncovered in a single garment and objected to it. (Sunan al-Kubra lil-Bayhaqi, vol. 2, p. 236)

Commentary:
Note:
(In the chain of narration, Khaythamah ibn Abi Khaythamah Abu Nasr Basri is weak in hadith transmission.)

Benefits and Issues:
From this, it is understood that apart from the middle days of the month, any three days can be observed as fasts, because the Prophet (sallallahu alayhi wa sallam) would sometimes fast three days without specifying or designating particular days, so that it would not be considered obligatory. In this way, sometimes he (sallallahu alayhi wa sallam) would fast three days at the beginning of the month; thus, those Companions (radi Allahu anhum) who were aware of these initial days narrated accordingly. Therefore, there is no contradiction between fasting on the white days (ayyam al-beedh) and fasting at the beginning of the month.

However, it is preferable to fast the three days of the white days (ayyam al-beedh), because the Prophet (sallallahu alayhi wa sallam) commanded this, as has been mentioned in hadith number 1707.