The World Federation Islamic Laws

Ritual 387

If an animal for sacrifice is bought in the belief that it is healthy, but it transpires that it is weak, it will still be sufficient, regardless of whether or not he found out that it was not sound before or after killing it.

If he already owns the animal, which he slaughtered under the pretext that it was sound, and it appeared that it was not, it is not sufficient, as a matter of ihtiyat.