It is narrated from Sayyiduna Ali (may Allah be pleased with him) that the Prophet (peace and blessings of Allah be upon him) forbade sacrificing an animal with a broken horn or a cut ear. The narrator says: I asked Sa'id bin al-Musayyib (may Allah have mercy on him) about its meaning, so he said: The animal whose half or more of the ear is cut.
Hadith Referenceمسند احمد / مسند الخلفاء الراشدين / 791