In Baghdad there was a man called Abu Hasan. Every evening he brought one stranger home and fed him well. Only, he never invited the same man twice.
A man who had come once was a stranger again the next day. That was his rule. Only that way, he believed, would he fall out with nobody. As long as he kept the rule he did not have one friend.
One evening the guest he brought in was dressed as a merchant. Abu Hasan had no idea who he was. It was the caliph Harun al-Rashid, out in the streets at night.