Qays bin Ubad (may Allah have mercy on him) said: I and al-Ashtar came to Sayyiduna Ali (may Allah be pleased with him), and we said: "O Ali! Did the Messenger of Allah (peace and blessings be upon him) entrust you with anything that he did not entrust to the people?" He said: "No, except what is in this document of mine." And in it was: "The blood of the Muslims is equal (in value), and they are as one hand against those besides them."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13763