When someone wants to sacrifice on the tenth of Dhu'l-Hijja, he is prohibited from cutting any of his hair or nails until he has sacrificed

Riyad as-Salihin (The Meadows of the Righteous)

by Imam Nawawi

313. Chapter: When someone wants to sacrifice on the tenth of Dhu'l-Hijja, he is prohibited from cutting any of his hair or nails until he has sacrificed

1706. Umm Salama reported that the Messenger of Allah, may Allah bless him and grant him peace, said, "If anyone has an animal to sacrifice and the new moon of Dhu'l-Hijja comes, he should not cut his hair or nails until he has sacrificed." [Muslim]