What is the ruling on someone who intended to offer a sacrifice (udhiyah) and then cut their hair or nails after the beginning of Dhul-Hijjah, whether forgetfully, ignorantly, or knowingly? Does this affect the acceptance of the sacrifice? And is it obligatory to verbally express the intention at the time of slaughter if the sacrificer is not slaughtering the animal themselves?

Most scholars dislike for the one intending to offer a sacrifice (udhiyah) to take anything from his hair or trim his nails during the first ten days of Dhul-Hijjah. This is a karahah tanzihiyyah (dislike of avoidance) until he offers the sacrifice. If someone does so intentionally or forgetfully, there is no sin upon him, and it does not affect the validity of the sacrifice. He should seek Allah’s forgiveness. As for articulating the intention at the time of slaughtering by saying: "O Allah, this is from You and for You" or "O Allah, accept it from me," there is no harm in it, and Ibn Qudamah considered it among the good practices.