The Book of Sacrifices
35/7. Chapter:
When the first ten days of Dhul-Hijjah begin, it is forbidden for the one who wants to offer a sacrifice to remove anything from his hair, nails or skin
Sahih Muslim
وَحَدَّثَنِي عُبَيْدُ اللَّهِ بْنُ مُعَاذٍ الْعَنْبَرِيُّ، حَدَّثَنَا أَبِي، حَدَّثَنَا مُحَمَّدُ بْنُ عَمْرٍو اللَّيْثِيُّ، عَنْ عُمَرَ بْنِ مُسْلِمِ بْنِ عَمَّارِ بْنِ أُكَيْمَةَ اللَّيْثِيِّ، قَالَ سَمِعْتُ سَعِيدَ بْنَ الْمُسَيَّبِ، يَقُولُ سَمِعْتُ أُمَّ سَلَمَةَ، زَوْجَ النَّبِيِّ صلى الله عليه وسلم تَقُولُ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " مَنْ كَانَ لَهُ ذِبْحٌ يَذْبَحُهُ فَإِذَا أُهِلَّ هِلاَلُ ذِي الْحِجَّةِ فَلاَ يَأْخُذَنَّ مِنْ شَعْرِهِ وَلاَ مِنْ أَظْفَارِهِ شَيْئًا حَتَّى يُضَحِّيَ " .
Umm Salama, the wife of Allah's Apostle (ﷺ), reported Allah's Messenger (ﷺ) to have said: He who has a sacrificial animal with him whom (he intends) to offer as sacrifice, and he enters the month of Dhu'I-Hijja, he should not get his hair cut or nails trimmed until he has sacrificed the animal.
Reference : Sahih Muslim 1977gIn-book reference : Book 35, Hadith 57USC-MSA web (English) reference : Book 22, Hadith 4873