Umm Salama reported (these words) directly from Allah's Messenger (ﷺ):
If anyone has in his possession a sacrificial animal to offer as a sacrifice (on 'Id al-Adha), he should not get his hair cut and nails trimmed after he has entered the first days of Dhu'l Hijja
Reference: Sahih Muslim 1977 d In-book : Book 35, Hadith 55 USC-MSA web (English) : Book 22, Hadith 4871 (deprecated)
Help us gift a modern, ad-free Islamic application for the Muslim Ummah. Your donation will be recorded as Sadaqah Jariyah in your book of deeds, In Sha Allah.