Ja'far bin Muhammad narrates from his father that the Prophet (peace and blessings be upon him) named Sayyiduna Hasan bin Ali (may Allah be pleased with them both) on the seventh day after his birth, and that it was he (peace and blessings be upon him) who derived the name "Husayn" from the name "Hasan." And the narrator mentioned that between (the births of) the two brothers there was only the span of a pregnancy.