What do the pious and expert scholars of Islam say: What is the permissibility regarding the cutting of a man’s hair, after he has passed away?
It is not allowed. It is mentioned in Durr al-Mukhtar that the hair of the deceased is not to be combed, meaning that this act is considered Makruh Tahrimi. Furthermore, the nails of the deceased are not to be clipped, except for a nail that is broken, nor should the hair be shaved off, nor should he be circumcised. Under the topic of sacrifice, it is mentioned in Radd al-Mukhtar, that it is not permissible to groom, comb or cut the hair of the deceased.
And Allah ﷻ knows best
Imam Ahmad Rida Khan رحمة الله تعالى عليه
Translation by Dr Musharraf Hussain Al-Azhari Translator of Majestic Quran, www.majesticquran.co.uk