Is it a Sunnah not to cut the nails and beard for ten days if the person is sacrificing an animal on his behalf on Eid al-Adha.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Everyone who intends to offer a sacrifice has to refrain from clipping nails and cutting hair after the beginning of the first ten days of Thul-Hijjah. It is forbidden for such a person to cut his hair or nails. The majority of the Muslim scholars believe that it is merely detestable for the Hadeeth narrated by Umm Salamah that the Prophet said: “When the first ten days of Thul-Hijjah start, one who intends to offer a sacrifice should not have his hair cut or his nails trimmed, till he/she has offered his/her sacrifice.” [Muslim]

It is reported in a narration that he should not remove any hair of his skin. The wisdom behind the above ruling is for all the parts of the body to remain freed from Hellfire.

If one cuts his/her hair or nails, he/she has to ask forgiveness of Allah only and does not have to pay any expiation.

Allah knows best.