Umm Salamah (May Allah be pleased with her) said:
The Messenger of Allah (ﷺ) said, "When anyone of you intends to sacrifice the animal and enter in the month of Dhul-Hijjah, he should not get his hair cut or nails pared till he has offered his sacrifice."
[Muslim].
عن أم سلمة رضي الله عنها قالت قال رسول الله صلى الله عليه وسلم : "من كان له ذبح يذبحه، فإذا أهل هلال ذي الحجة، فلا يأخذن من شعره ولا من أظفاره شيئًا حتى يضحي" ((رواه مسلم)).
Sunnah.com reference : Book 18, Hadith 196
Arabic/English book reference : Book 18, Hadith 1706