Because when the Prophet Muhammad (peace be upon him) clarified that it is not permissible to offer sacrifice of four types of animals, this is evidence that it is permissible to offer sacrifice of animals other than these.

It is narrated from Sayyiduna Ali (may Allah be pleased with him) that the Prophet of Allah (peace and blessings be upon him) forbade sacrificing an animal with a broken horn or a cut ear. Imam Qatadah (may Allah have mercy on him) says: I narrated this tradition to Imam Sa'id bin al-Musayyib (may Allah have mercy on him), so he said: By "‘adhb" is meant an animal whose half horn is broken or half ear is split. Janab Shahr bin Hawshab says: By "‘adhb" is meant a horn that is broken from the inside.