Musannaf Ibn Abi Shayba 28:573

Abdullah ibn Bakr al-Sahmi narrated to us, he said: Hatim ibn Abi Saghirah narrated to us, from al-Nu’man ibn Salim, that ‘Amr ibn Aws informed him, from his father, who said: We were sitting with the Messenger of Allah (may Allah bless him and grant him peace) while he was preaching to us and reminding us, when a man came to him and asked him. The Messenger of Allah (may Allah bless him and grant him peace) said: "Go and kill him." When the man turned away, the Messenger of Allah (may Allah bless him and grant him peace) called him and said: "Do you testify that there is no god but Allah?" He said: "Yes." He said: "Go and let him go." "I have only been commanded to fight the people until they say: 'There is no god but Allah.' If they do that, their blood and their wealth become inviolable to me."