It is desirable for the one who will be sacrificing an animal for Qurbānī to avoid cutting their hair or nails until after the animal is slaughtered. Rasulullah salallahu alayhi wasallam said:
“When the ten days (of Zul-Hijjah) begin and a person has an animal for sacrifice which he intends to slaughter, then let him not cut his hair or trim his nails.” (Muslim)
Rasulullah salallahu alayhi wasallam said in another Hadith:
“Whoever has an animal for slaughtering, once the crescent of Zul- Hijjah has been declared he should not cut his hair or trim his nails until he has sacrificed (the animal)” (Muslim)
It is a recommended act due to the Hadīth. However, if one did cut his hair and/or nails during the first ten days of Zul-Hijjah before sacrificing, it will not affect the validity of making Qurbānī.
Allah-Ta’aala has taken oath of the night in Suratul-Fajr of the Quraan.
Nabi (S.A.W) has said: “There is no better time to perform Ibaadah(devotion) to Alaah that on the (first) ten days of Zul Hijjah. A Day’s fast in it, equals the fast of a year, and a night’s Ibaadah in it, equals the Ibaadah of Laylatul Qadr”.- Tirmizi Ibn Majah.
According to the majority, the ten nights are those of the ten days of Zul-Hijjah, especially the ninth, which is the day of Arafah and night preceeding the eid day. All these days are filled with special virtues.
The observance of the fast of the ninth of Zul-Hijjah is a atonement of the past and coming year, and to remain awake on the night of Eid and perform Ibaadah is a source of great virtue and thawaab.
Source: www.jamiat.org.za