Wearing Pants Is not Haram. It is not a Kuffar Dress Rather it is Customary dress.
A Question Asked to The scholars of the Standing Committee for Issuing Fatwas were asked about the imitation of the kuffaar that is forbidden.
What is meant by the imitation of the kuffaar that is forbidden is resembling them in the customs that are exclusive to them, or in the religious beliefs and acts of worship that they have invented, such as imitating them by shaving the beard.
With regard to “wearing pants, suits and so on, the basic principle is that all types of clothing are permissible”, because this is the matter of customs. Allaah says (interpretation of the meaning):
“Say (O Muhammad): Who has forbidden the adornment with clothes given by Allaah, which He has produced for His slaves, and At-Tayyibaat [all kinds of Halaal (lawful) things] of food?”
An exception from that is made in the case of that for which there is shar’i evidence that it is forbidden or makrooh, such as silk for men, or that which shows the ‘awrah because it is thin and shows the colour of the skin beneath it, or because it is tight and shows the shape of the ‘awrah, because in that case it is like showing it, and showing it is haraam. Similarly, clothing which is worn exclusively by the kuffaar is not permitted for men or for women, because the Prophet (peace and blessings of Allaah be upon him) forbade imitating them. And it is not permitted for men to wear women’s clothing or women to wear men’s clothing, because the Prophet (peace and blessings of Allaah be upon him) forbade men to imitate women and women to imitate men.
Wearing pants or trousers is not something that is exclusive to the kuffaar, because that is something that is worn by both Muslims and kaafirs in many countries. Rather some people do not like to wear such things in some countries because they are not used to it and it is contrary to the customary dress of the people, even though it is customary among other Muslims. But if the Muslim is in a country where the people are not accustomed to such clothing, it is better for him not to wear it when praying or in public gatherings or in the street. End quote.
(Fataawa al-Lajnah al-Daa’imah, 3/307-309)