"إذا رأيتم هلال ذي الحجة وأراد أحدكم أن يضحي ¤ فليمسك عن شعره وأظفاره"
The Prophet (peace and blessings be upon him) said:
"When you see the new moon of Dhul-Hijjah and one of you intends to offer a sacrifice, let him refrain from (cutting) his hair and his nails (until he has sacrificed)."
Hadith Referenceصحیح الجامع الصغیر / حرف الألف / 574