Musannaf Ibn Abi Shaybah 36020 — The affair of al-Qadisiyyah

Al-Harith said: Sayyiduna Umar (may Allah be pleased with him) passed by the people of Nakha' and counted them, and they were two thousand five hundred. Their leader was named Artah. Sayyiduna Umar said: "I see nobility settling among you. Go to your brothers in Iraq." They said: "No, we will go to Syria." Sayyiduna Umar said: "Go to Iraq." They said: "There is no compulsion in religion." Sayyiduna Umar said: "Go to Iraq." So they went to Iraq, and there they began seizing foals and slaughtering them. Sayyiduna Umar wrote to them: "Put things right, for in this matter there remains a refuge or breathing room."