Sayyida Umm Salamah (may Allah be pleased with her) narrates: The Prophet Muhammad (peace be upon him) said: "Whoever intends to offer a sacrifice, when the new moon of Dhul-Hijjah is sighted, he should not cut his hair nor trim his nails until he has offered the sacrifice."
Hadith Referenceصحیح ابن حبان / كتاب الأضحية / 5917
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح: م - انظر ما قبله.فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده حسن