[Is wearing trousers and the necktie imitation of the unbelievers?]

The answer – and Allah is the One who grants success – is that imitation has come to be prohibited in an unrestricted way, without being confined to something specific. He, Exalted, said: "O you who have believed, do not be like those who disbelieved..." [Āl ʿImrān:56], and likewise in the Sunnah. And wearing trousers and the necktie today is no longer a dress specific to the unbelievers, as appears; therefore, wearing that is not considered imitation of the unbelievers. Likewise, shaving the beard is not something specific to the unbelievers, so the one who shaves his beard is not considered an imitator of the unbelievers.

Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2