What is the evidence used by those who say that a man's navel is 'awrah?

The navel of a man is not considered 'awrah (private parts) according to the majority of scholars. Among the Shafi'is, there is a view that it is 'awrah, but the correct position within their school of thought is that it is not 'awrah. The proof that the navel is not 'awrah is the saying of the Prophet (peace and blessings be upon him): "The 'awrah of a man is what is between his navel and his knee." Abu Hurayrah also kissed the navel of Al-Hasan, and if it were 'awrah, they would not have done that. As for the evidence of those who hold that the navel is 'awrah, it includes the argument that since it is one of the boundaries of the 'awrah, it must be part of it, or because looking at it might arouse desire.