Abu Ishaq told that Ali looked at his son al-Hasan and said: This son of mine is a sayyid (chief) as named by the Prophet (ﷺ), and from his loins will come forth a man who will be called by the name of your Prophet (ﷺ) and resemble him in conduct but not in appearance. He then mentioned the story about his filling the earth with justice.
Sunan Abi Dawud Book 38, Hadith 12