Answered by Shaykh Amjad Rasheed
What are the proper manners (adab) of clothing for men? Is Western clothing considered something suitable for a religious Muslim to wear if he lives in the West?
Certain manners related to dress are obligatory and others are recommended. What is obligatory is to cover the nakedness which, for men, is everything between the navel and knee. That which covers the nakedness must be something that conceals the colour of the nakedness [h. i.e., one must not be able to tell whether the underlying skin is black or white], so a thin cloth through which the colour of one’s nakedness can be seen is insufficient.
As for the recommended manners, it is that the clothing be loose-fitting and that it not reveals the shape of one’s nakedness. Whenever a Muslim [h. man] achieves these three manners with regard to his clothing, they suffice him even if the clothing is Western, such as a Western suit.
It is sunna for everyone (as mentioned in the Tuhfa in the chapter of clothing), and an emphasized sunna for someone who is an exemplar for others to beautify their appearance and garments and to look extremely handsome and clean.
– Amjad Rasheed
(Translated by Hamza Karamali)