It is narrated from Umm Salamah (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) said: "When the first ten days of Dhul-Hijjah begin and any one of you intends to offer a sacrifice, then he should not cut anything from his hair or skin (nails)."
Hadith Referenceمسند الإمام الشافعي / كتاب العيدين والأضاحي والاستسقاء / 503
Hadith Takhrijاخرجه مسلم، الأضاحي، باب نهى من دخل عليه عشر ذي الحجة .... الخ (1977)۔