Musannaf Ibn Abi Shayba 36:96

'Abd al-Rahim ibn Sulayman narrated to us, from Isma'il ibn Abi Khalid, from Qays ibn Abi Hazim, who said: The Messenger of Allah (may Allah bless him and grant him peace) sent [an expedition] to Khath'am, to some people who were among them. When the Muslims reached them, they sought protection through prostration. He said: So they prostrated. He said: Then some of them were killed. That reached the Messenger of Allah (may Allah bless him and grant him peace), so he said: "Give them half of the blood money because of their prayer." Then the Prophet (may Allah bless him and grant him peace) said: "Behold, I am free of every Muslim who resides among the polytheists."