What is the criterion for the prohibition of imitating the disbelievers?

Question : What is the criterion, I mean, for strictness? We must address the matter.

Answer : Imitating them in their acts of worship is forbidden in all cases, even if it becomes widespread among Muslims. Imitating them in acts of worship, such as imitating them in giving the salam or returning the salam, is forbidden because the salam is an act of worship.
As for customs, the scholars (may Allah have mercy on them) mentioned that if the ruling in a matter is tied to a cause,
its ruling is lifted when the cause is removed. So if the cause of this action, or this clothing, or this bedding is imitation,
and this matter becomes widespread among people so that there is no distinction between the Muslim and the disbeliever, then the ruling is lifted, because what is established by a cause is removed when that cause is removed. Al-Hafiz Ibn Hajar (may Allah have mercy on him) mentioned this in Fath al-Bari, citing it from Malik, and this is correct. Yes.