All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
Scholars differed as to whether a sacrificial animal, which becomes defective after having been specified and before getting slaughtered, will it clear the liability as a sacrifice or not. They had two opinions on this issue. The sound and preponderant opinion is that such an animal will clear the liability as a sacrifice, as expressed by the majority of scholars. In Al-Mughni, Ibn Qudaamah said, “If an animal that is free from defects is assigned as a sacrifice and then it got some defect that prevents it from serving as a (perfect) sacrifice, then it can be slaughtered as a sacrifice and the liability is cleared. This was reported on the authority of ‘Ataa’, Al-Hasan, An-Nakha‘i, Az-Zuhri, Ath-Thawri, Maalik, Ash-Shaafi‘i and Is-haaq.”
This is evidenced by a citation on the authority of Ibn Az-Zubayr that a one-eyed she-camel was brought among his sacrificial animals. Therefore, he said, “If she became defective after you had bought her, then approve her. If she was defective before you bought her, then replace her.” [An-Nawawi: Authentic chain of narrators]
Shaykhul-Islam Ibn Taymiyyah said, “If a (sound) animal is bought to be sacrificed and it got some defect before getting slaughtered, it can be slaughtered as a sacrifice, according to one of the two statements of scholars.”
A sheep that has been assigned as a sacrifice and then got some defect will clear the liability as a sacrifice on two conditions:
First: The defect should not be caused by carelessness of the one who offers the sacrifice.
Second: The relevant sheep must not have been assigned to serve as a sacrifice to which one was liable before specifying it. That is if someone vowed to slaughter a sacrifice then specified a sheep to serve as a sacrifice for the vow, then the sheep became defective, then it will not clear his liability. This is because such a person was under the obligation of fulfilling the vow, and thus nothing but a sound animal would serve as a sacrifice. However, if someone initially assigned a sheep for sacrifice then it got some defect that is not caused by his carelessness, then the sheep will serve as a sacrifice as we have mentioned on the authority of many scholars.
Allaah Knows best.