It is narrated from Sayyidah Umm Salamah (may Allah be pleased with her) that the Prophet (peace and blessings be upon him) said: "Whoever is reached by the month of Dhu al-Hijjah while he has a sacrificial animal that he intends to slaughter, let him refrain from (cutting) his hair and his nails."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 20227