Is an Udhiyah permissible for one who removes some of his hair or nails during the first ten days of Dhul-Hijjah?

Your brother is not bound by anything from the past as long as he did not intend to offer a sacrifice. If he intended to sacrifice, the ruling of abstaining [from cutting hair and nails] becomes applicable from the moment of intention. The sacrifice is permissible even if a person did not intend it during the first ten days [of Dhul-Hijjah].

Scholars have differed regarding the ruling on abstaining from cutting hair and nails for one who intends to offer a sacrifice. Some have prohibited it, while others have considered it disliked (makrooh tanzeeh).

It is more prudent to abstain from cutting hair and nails to avoid the disagreement. Whoever has cut something is required to seek forgiveness, and there is no expiation (fidyah) upon him. Cutting hair does not affect the validity of the sacrifice.