Muslim

Hadith Commentary:
An objection arises here as to how the Prophet (sallallahu alayhi wa sallam) wore these robes when they were made of silk.
The answer is that perhaps, until that time, silk garments had not yet been declared unlawful (haram) for men, or the Prophet (sallallahu alayhi wa sallam) may have placed the robe over himself for protection, which does not constitute wearing it in the usual sense—just as someone might do so before giving it to another. After this, silk garments were made unlawful (haram) for men.

Hadith Commentary:
It is understood from the narrations that the Messenger of Allah (sallallahu alayhi wa sallam) led the Maghrib prayer wearing a silk robe. After concluding the prayer with salam, he quickly took it off and threw it aside. The noble Companions (radi Allahu anhum) asked:
O Messenger of Allah! You wore it and then performed prayer in it, so you gave the aforementioned reply.

Ibn Battal (rahimahullah) says that he (sallallahu alayhi wa sallam) took it off quickly because the use of silk was forbidden for men, and this robe was pure silk, or he took it off because it was the dress of non-Arabs.

It is mentioned in the hadith:
“Whoever imitates a people is one of them.”
(Sunan Abi Dawud, Book of Clothing, Hadith: 4031)

In any case, silk is forbidden for men and permissible for women, which will be explained further ahead.
(Fath al-Bari: 10/334)

Hadith Commentary:
➊
According to Imam Bukhari rahimahullah, if a person performs prayer while wearing a garment of silk, his prayer will be valid.
He will certainly incur the sin of wearing silk, because its wearing is forbidden (haram) for men.
Just as it is forbidden for a person in the state of ihram to wear stitched clothing, but if he does wear it and performs prayer, his prayer will still be valid.
The harm that results from such incidental factors is expressed as reprehensibility (karahah).
Thus, Allamah Khattabi rahimahullah says that the prayer of one who performs it while wearing a silk garment is valid, although according to us it is reprehensible (makruh).
(I’lam al-Hadith: 1/357)
It should also be clarified that the silk cloak in which the Messenger of Allah sallallahu alayhi wa sallam performed prayer was a gift from Akidar ibn Abd al-Malik, the king of Dumat al-Jandal.
(Sahih Muslim, Kitab al-Libas, Hadith: 5422 (2071))
In Sahih Muslim as well, there is mention of a silk robe (qaba’ dibaj).
It is clarified therein that the Messenger of Allah sallallahu alayhi wa sallam was prohibited from it by Jibril alayhis salam.
(Sahih Muslim, Kitab al-Libas, Hadith: 5419 (2070))
Therefore, it is possible that this prayer was performed before the prohibition of wearing silk was revealed, and when you became aware of its prohibition, you removed it from your body with displeasure.
And if you removed it before this prohibition, then it means that even before the prohibition and interdiction, you were attentive to what pleases Allah, the Exalted.

➋
It can also be said that as long as you had not used silk, you were not aware of its defect and harm; when you used it, its defect became apparent—that it is the clothing of those who pursue luxury, and its use brings softness to the body, which is contrary to masculine toughness and endurance.
A man’s body should be strong; therefore, when you removed it, you said:
“This is not the clothing of the God-fearing, but the clothing of those who pursue luxury, so it should be avoided.”
It should be noted that the Shariah has permitted the use of silk in certain cases of necessity, for example:
During jihad, it is permissible to use silk under armor, so that if the enemy’s sword cuts through the armor, it will be rendered ineffective by the silk.
If there is no other garment, it may be used for covering the private parts (satr) or for protection from cold.
If, due to roughness of the body, dry itching or lice occur, it may be worn for treatment.
Other related issues will be discussed in the Book of Clothing (Kitab al-Libas),
by the permission of Allah, the Exalted.

771. Commentary: Wearing silk is unlawful (haram) for men. Performing prayer (salah) in it will be even more disliked. The Messenger of Allah (sallallahu alayhi wa sallam) must have worn it before its prohibition. Then, due to its being disliked, he removed it. It is not the case that he wore or removed it after it became unlawful. His words: «لَا يَنْبَغِي هَذَا لِلْمُتَّقِينَ» are also evidence that this incident occurred at a time when silk had not yet been made unlawful. After its prohibition, both the pious and the impious are equal (in obligation), however, there is no need to repeat a prayer performed while wearing silk, because nothing within the prayer itself has been corrupted, nor has any of its conditions or pillars been omitted. The prohibition of silk is a separate issue from the prayer; thus, the sin of wearing silk is one matter, and the validity of the prayer is another matter.