بسم الله الرحمن الرحيم
Hadhrat Umm Salma (رضي الله تعالى عنها) narrates that the holy Prophet Muhammad (صلى الله عليه وسلم) said: One who intends to do qurbani (sacrifice) then he should not get his hair cut or nails trimmed in the month of Dhul Hijjah until he sacrifices the animal. (Muslim: 2:160)
It was learnt that a person who has not cut his hair or nails due to the intention of qurbani from the first day of Dhul Hijjah to the days of qurbani then he may cut his hair and nails whenever he wishes after sacrificing the animal as this ruling is only up to the qurbani nor up to the complete days of qurbani.
It is imperative to note that as per the Islamic Shariah it is haram and unlawful and major sin to shave the beard or keep it less than one fist length.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.