Sayyiduna Ali (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) ordered us to examine the eye and the ear of the sacrificial animal carefully, and not to sacrifice an animal whose ear is torn from the front or from the back, or slit, or pierced with a round hole.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19102