The Prophet ﷺ said, "Whoever sees the crescent of Dhul-Hijjah and intends to offer a sacrifice should not cut any of his hair or nails until he has offered the sacrifice."
أخبرنا سليمان بن سلم البلخي قال حدثنا النضر وهو ابن شميل قال أنبأنا شعبة عن مالك بن أنس عن ابن مسلم عن سعيد بن المسيب
عن النبي ﷺ قال من رأى هلال ذي الحجة فأراد أن يضحي فلا يأخذ من شعره ولا من أظفاره حتى يضحي
Muslim narrated it in the Book of Sacrifices, Chapter on the prohibition of one who enters the ten days of Dhul-Hijjah intending to make a sacrifice from taking anything from his hair or nails, hadith 41/1977, from the hadith of Shubah with the same wording, and it is found in Kubra, hadith 4451.