Assalaamu alaykum. Was the clothing of Prophet Muhammad, sallallaahu 'alayhi wa sallam, Sunnah or just a customary practise of the Arabs? I watched a video of Dr. Yasr Qadhi in which he says that the Sunnah, when it comes to dressing, is to accommodate the culture of your people as much as possible, as long as the Shariah allows you to do so.
Link: https://www.youtube.com/watch?v=QQPmm3XY7-c
Moreover, Sheikh Muhammed Salih Al-Munajjid said, “If covering the head is customarily regarded as a part of adornment in a particular country, then the head should be covered, otherwise it does not have to be covered.”
Link: https://islamqa.info/en/243699%
People in my locality wear shirts and trousers, so why do the practising Muslims and scholars in my locality wear a cap and long Kurta pyjamas? If it is from the culture of the people of my locality to wear shirts and trousers, then why do the scholars and practising Muslims go against that cultural dress? Please explain this issue to me in detail. It is very important to me. I want to follow the sunnah of Prophet Muhammad, sallallaahu 'alayhi wa sallam, and not the customary practices of the Arabs of that time. May Allah reward you.

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.

The Prophet wore the clothes that his people were wearing.

Shaykh Ibn ‘Uthaymeen said:

“The basis for what the Prophet did as a matter of habit is to follow the habits of his people; that is to say that a man does what the people are accustomed to doing, such as wearing the turban and the Izaar (waist sheet) and Ridaa' (upper garment). The Prophet used to wear the turban, and he used to wear the Izaar and Ridaa', but he did this as a habit, meaning that the people in his time were accustomed to wearing this. The ruling in this regard is that a man follows the custom of his country unless that custom is prohibited (in Islam)...”

The qamees is not a garment that is peculiar to the Arabs; rather, it also existed in the past Arab nations. The Prophet of Allah Yoosuf (Joseph), may Allah exalt his mention, used to wear it.

Al-Bukhaari wrote a chapter in his Saheeh which he entitled, “Chapter: Wearing the qamees and the saying of Allah about Yoosuf: {Take this, my shirt, and cast it over the face of my father; he will become seeing.} [Quran 12:93]”

The interpreters of the Quran said, “He mentioned this verse as an indication that wearing the qamees was an old custom.”

With regard to the short qamees worn by our Muslim brothers in Asian countries, then it also belongs to the same category of qamees, and the Companions, may Allah be pleased with them, used to wear it, as At-Tabaraani narrated in Al-Mu’jam from Abul-Mutawakkil that he saw Ibn ‘Umar wearing an Izaar that reached the middle of his shin and that his qamees was shorter than his Izaar.

It was also narrated that the Prophet used to wear a short qamees with short sleeves. [Ibn Maajah with a weak chain of narrators, and some scholars classified it as Hasan (good) based on its total ways of narration]

There is no doubt that the dress depends on the custom; so a man wears what people are used to wearing as long as it is permissible and does not differ from what they wear so as not to fall into seeking fame.

Shaykh Ibn ‘Uthaymeen said:

“A person is commanded to wear what is worn by people unless it is prohibited, because if he wears clothes that are different from what the people wear, then he gains fame and distinction for wearing them, unless he is in a foreign country and the clothing of the people of this country is different from the dress of this man who came to them. In this case, it is acceptable that he keeps wearing his clothes that he used to wear in his own country because the people know that he is a stranger and it is not surprising that his clothes are different from theirs. This is the case now in our country, especially in Makkah and Madeenah, where people wear their own clothes that they used to wear in their own country, and no one denies that from them...”

However, wearing the qamees in the West or other countries whose people do not wear the qamees is not considered a means of seeking fame, and it is not included in the dispraised act of dressing differently than the people, because wearing the qamees in itself is a desirable Sunnah, for the hadeeth of Umm Salamah, may Allah be pleased with her, who related, “The most beloved of the clothes to the Prophet was the qamees.” [Abu Daawood and At-Tirmithi]

Ash-Shawkaani said in Nayl Al-Awtaar, “The hadeeth indicates that it is recommended to wear the qamees.”

It is for this reason that the jurists stated that it is desirable to wear the qamees.

Kash-shaaf Al-Qinaa’ reads, “It is a Sunnah to wear the qamees because Umm Salamah, may Allah be pleased with her, said, ‘The most beloved of the clothes to the Prophet was the qamees.’”

The jurists also stated that it is desirable to wear the Sirwaal (a form of baggy trousers); Kash-shaaf Al-Qinaa’ also reads, “It is desirable to wear Sirwaals because Ahmad narrated from Abu Umaamah that he said, ‘We said, 'O Messenger of Allah, the people of the Book wear trousers and do not wear Izaar.'’ So he said, 'Wear trousers, and wear Izaar, and be different from the People of the Book.'’”

Therefore, wearing the qamees and wearing trousers is a desirable Sunnah, and it is not considered dressing for fame, because the criterion for the dress of fame according to the scholars is wearing clothes that are different from the clothes of the people of his own country without an excuse, and that wearing it undermines his character. Ibn Muflih, from the Hanbali School, said in Al-Aadaab Ash-Shar’iyyah, “...and wearing clothes that are different from the clothes of his own country without an excuse … and it was said that the dress of fame (Libaas Shuhrah) is what differs from the clothes of his country and that it undermines him.”

Some scholars added the condition of intention in wearing a dress of fame, as stated in Al-Insaaf by Al-Mirdaawi, quoting Shaykh Ibn Taymiyyah, “It is forbidden to wear a dress of fame, which means the clothes intended to show pride or to show off modesty...”

Therefore, whoever wears a qamees as a way of imitating the Prophet and not with the intention of pride or with the intention of showing off his modesty, then he will be rewarded, Allah willing, even if the people do not wear it frequently; this does not fall under the category of the dress of fame.

It should be mentioned that if someone fears to be harmed in a society where people do not wear the qamees and wanted to soften their hearts for Da‘wah (proselytization), then he may wear the same clothing as them. Rather, some jurists stated that it is desirable for him to wear the same dress as them.

Shaykh Ibn Taymiyyah said:

“If a Muslim is in a land of war or in a non-Muslim land that is not at war (with the Muslims), he is not commanded to differ from them in the outside appearance for the harm that he may face. Rather, it is desirable for a man or even a must sometimes to share their apparent custom if there is a religious benefit in it, such as calling them to the religion and knowing their intentions in order to inform the Muslims about that, or in order to repel their harm from the Muslims, and other good intentions. As regards in the land of Islam and the land of Hijrah (migration), where Allah gave glory to His Religion and made the non-Muslims inferior (to the Muslims) and commanded them to pay the Jizyah (tax), then being different from them (the disbelievers) is legislated.”

Allah knows best.