Is it permissible to shave the head or mustache or trim the nails during the first ten days of Dhul-Hijjah for one upon whom the Udhiyah (sacrifice) is obligatory, and who is the person upon whom the Udhiyah is obligatory?

The Udhiyah (sacrifice) is a confirmed Sunnah according to the majority of scholars. It is not obligatory except by virtue of a vow, or by designation such as purchasing a sheep or intending it for sacrifice, or if the deceased bequeathed it, in which case it becomes obligatory from one-third of his wealth. As for trimming hair and clipping nails for one who intends to offer a sacrifice, the answer to that has been provided previously.