Sunan Ibn Majah, Chapter: The Chapters on Tribulations

that his father, Aws, told him: that his father, Aws, told him:"We were sitting with the Prophet (saw) and he was narrating to us and reminding us, when a man came and spoke privately to him. He said: 'Take him away and kill him.' When the man turned away, the Messenger of Allah (saw) called him back and said: 'Do you bear witness that none has the right to be worshiped but Allah?' He said, 'Yes.' He said: 'Then go and let him go, for I have been commanded to fight the people until they say: La ilaha illallah, then if they do that, their blood and wealth are forbidden to me.'"