Is it true that there are some days when it is not permissible for a Muslim to cut nails, hair, or wear new cloths? If yes, then what are those days and what are forbidden things during those days?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

It is lawful to cut one's hair and one's nails at anytime except in two times:

First, when the person assumes the state of Ihram for a Hajj or ‘Umrah until he or she quits this state; it is forbidden for him or her to cut their hair or nails.

Second, when the month of Thul Hijjah starts, any person intending to slaughter a sheep on ‘Eed day as a sacrifice should abstain from cutting his hair or nails as doing so is dislikable.

As for wearing new or old clothes, this is permissible at anytime provided the garment is not too tight and that it meets all the other Sharee’ah conditions…etc.

But if the person assumes the state of Ihram for Hajj or ‘Umrah, he should not then wear any knit (form-fitting) clothes that fit the body such as shirts, trousers …etc.

Allah knows best.