What is the ruling on selling and gifting forbidden garments, such as trousers and shirts, and what should a person do about what they have already sold or what remains with them of such items?

It is permissible to buy, sell, and gift clothes. The basic principle is permissibility, with the exception of clothes designated for unlawful purposes (such as silk for men), or clothes that are known or highly likely to be used for unlawful purposes (such as women's immodest display).

In the case of selling clothes used for unlawful purposes, one must repent for assisting in sin. The money earned from such sales is, according to the preponderant opinion of jurists, lawful, because the sale itself is valid even if it is prohibited.

As for the remaining clothes, the aforementioned rulings regarding buying, selling, and gifting apply to them.