Silsilat al-Ahadith al-Sahihah

Sayyiduna Ali (may Allah be pleased with him) says: When Hasan was born, I named him Hamzah, and when Husayn was born, I named him after his uncle Ja'far. (One day) the Messenger of Allah (peace and blessings of Allah be upon him) called me and said: "I have been commanded to change both of these names." I said: Allah and His Messenger know best. Then the Prophet (peace and blessings of Allah be upon him) named them Hasan and Husayn.