The Battle of Ayn al-Tamr took place in modern-day Iraq (Mesopotamia) between the early Muslim Arab forces and the Sassanians along with their Arab Christian auxiliary forces. The Muslims under Khalid ibn al-Walid's command soundly defeated the Sassanian auxiliary force, which included large numbers of non-Muslim Arabs who broke earlier covenants with the Muslims. According to non-Muslim sources, Khalid ibn al-Walid captured the Arab Christian commander, Aqqa ibn Qays ibn Bashir, with his own hands.

Then Khalid instructed the entire forces to storm the city of Ayn al-Tamr and slaughter the Persian inside the garrison after they breached. After the city has been subdued, some Persians had hoped that the Muslim commander, Khalid ibn al-Walid, would be "like those Arabs who would raid [and withdraw].".

However, Khalid continued to press further against the Persians and their allies in the subsequent Battle of Dawmat al-Jandal, while he left two of his deputy, Al-Qa'qa' ibn Amr al-Tamimi and Abu Layla, to lead a separate forces in order to intercept another Persian-Arab christians enemy coming from east, which led to the Battle of Husayd