Question: Also, he is asking about shaving [the head] during the [first] ten days of Dhul-Hijjah?
Response: This is prohibited if he wants to offer the udh.hiyah sacrifice. If he wants to offer the udh.hiyah sacrifice, then he must not cut [even] a nail or the hair, since the Prophet ﷺ said:
«When the month of Dhul-Hijjah comes, and any one of you wants to offer a sacrifice, [then] let him not remove anything from his hair and his nails.» and in another narration «…and nor anything from his skin».
So if he has affirmed [his intention] to offer the sacrifice for himself, or for himself and the members of his household, or for himself and his parents, then he must avoid the hair and nails. So he must not shave the hair [on his head], and nor should he cut his nails – based upon this authentic hadeeth.