Musannaf Ibn Abi Shayba 18:912

Abu Bakr narrated to us, he said: Shababa narrated to us, from Ibn Abi Dhi'b, from al-Muttalib ibn al-Sa'ib al-Sahmi, from Sa'id ibn al-Musayyib, that Uthman decreed that any two people who fight each other are responsible for what is between them.