The claim that the days of `Eid-ul-Adha are inviolable, where one should not shave their hair or wear new clothes

A: Regarding the first ten days of Dhul-Hijjah, the Prophet (peace be upon him) forbade whoever wants to offer an Ud-hiyah (sacrificial animal offered by non-pilgrims) from cutting any of their hair, nails, or skin from the body until the Ud-hiyah is offered. There is a Hadith narrated by Um Salamah (may Allah be pleased with her) which she attributed to the Prophet that states: When Dhul-Hijjah starts and anyone of you intends to offer Ud-hiyah (sacrificial animal offered by non-pilgrims), let them not cut anything of their hair or nails until they sacrifice it. It is permissible for those who will not offer Ud-hiyah to do any of the acts mentioned above that are forbidden for those who will offer Ud-hiyah.With regard to the Days of Tashriq (11th, 12th and 13th of Dhul-Hijjah), it is forbidden to observe Sawm (Fast) during them. They are days of eating and drinking as the Prophet (peace be upon him) pointed out. (Part No. 10; Page No. 436) With regard to forbidding the shave of hair on the Day of `Ashura’ (10th of Muharram), there is no evidence that supports such a prohibition. This also applies to the prohibition of wearing new clothes. The day of `Ashura’ should not be marked with either joy or sadness. We think that this is the other day meant by the person asking.The permissible act to do is to observe Sawm on the Day of `Ashura' along with a day before or after it according to the command of the Prophet (peace be upon him).May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.