From the Rulings on the Udhiyah

Question: Is the udhiyah for the family as a whole, or for each adult individual in it? When is it slaughtered? Is it a condition for the one who offers it that he not take anything from his nails or hair before slaughtering it? If it is for a woman who is menstruating, what is to be done? What is the difference between the udhiyah and charity in such a matter? Please inform us? May Allah reward you with good.

Answer: The udhiyah is a confirmed recommended practice (sunnah muakkadah). It is prescribed for the man and the woman, and it suffices for the man and his household, and for the woman and her household; because the Prophet (peace and blessings be upon him) used to sacrifice every year two white, horned rams, one on his behalf and on behalf of his household, and the second on behalf of those of his Ummah who had not sacrificed.
Its time is the Day of Sacrifice and the Days of Tashriq in every year. It is the recommended practice (sunnah) for the one who sacrifices to eat from it, to give it to his relatives and neighbors, and to give charity from it.
It is not permissible for one who intends to sacrifice to take anything from his hair, or from his nails, or from his skin, after the entry of the month of Dhu al-Hijjah until he sacrifices; due to the saying of the Prophet (peace and blessings be upon him): . It was narrated by Imam Muslim in his Sahih, from Umm Salama (may Allah be pleased with her).
As for the agent for the sacrifice, or for the endowment (waqf) in which there are sacrifices, it is not obligatory for him to refrain from taking his hair, or his nails, or his skin; because he is not the one sacrificing, rather this is upon the one who sacrificed who appointed him as his agent in that matter. Likewise, the one who established the endowment is the one who sacrificed. The overseer of the endowment is an executing agent and is not the one who sacrificed. And success is from Allah.