Does Cutting Hair in Dhul Hijjah Invalidate Udhiyah?
Question

If a person cuts his hair after the month of Dhul Hijjah has begun, and he intends to offer a sacrifice, is his sacrifice valid and will it be accepted?
Praise be to Allah.Shaykh Ibn Uthaymin (may Allah have mercy on him) said: 
“Yes, his sacrifice will be accepted but he will be a sinner. With regard to a widespread belief among the common people that if a man removes anything from his hair, nails or skin during the first ten days of Dhul Hijjah , his sacrifice is not valid, this is not correct, because there is no connection between the validity of his sacrifice and his removing anything from these three things .” (Al-Sharh al-Mumti’, 7/533) 
For more, please see these answers: 70291 , 70290 , and 33743 .
And Allah knows best.