The Muslim killed by Hz. Usama b. Zayd

Usama b. Zayd was a companion who was the son of Zayd b. Haritha, the freedman of the Prophet, and was loved by the Messenger of Allah like his own son. He was part of the group commanded by Ghalib b. Abdullah during the Murra Expedition (H. 8/M. 629). During the battle, Usama chased Mirdas b. Nahik from the Huraka branch of Banu Juhayna. Mirdas, facing death, said, 'There is no god but Allah, Muhammad is the Messenger of Allah.' Nevertheless, Usama killed the man. His justification was that the person might have said those words out of fear of death. When they returned to Medina, the Prophet learned of the incident. He called Usama and asked, 'Did you kill him after he said, 'There is no god but Allah'?' Usama replied, 'O Messenger of Allah! He said it out of fear of death,' to which the Messenger of Allah turned his face away and asked again, 'Why didn’t you check if he said those words sincerely or out of fear by looking into his heart?' The Prophet never forgot this incident. Usama narrated that the Prophet repeated the question 'Did you split his heart?' several times. Usama could never recover from the impact of this event and lived in regret until the end of his life. He swore that he would never kill anyone who says 'There is no god but Allah' from that day on, wishing he had not been a Muslim until that day. This incident reinforced an extremely important principle in Islamic law: If a person externally carries the signs of Islam, Muslims do not have the right to question their intention and treat them accordingly. A person is only responsible for their outward condition and behavior; only Allah knows the intentions in hearts. [Source: TDV Islamic Encyclopedia, 'Usama b. Zayd' article, islamansiklopedisi.org.tr/usame-b-zeyd; Bukhari, Maghazi 45; Muslim, Iman 155-158]