Musannaf Ibn Abi Shaybah

Hazrat Abdur Rahman, may Allah have mercy on him, narrates that when the news of the conquest of Tustar reached Hazrat Umar, may Allah be pleased with him... Tustar is a region of Basra... he, may Allah be pleased with him, asked those people: What news is there from distant places? The people replied: There was a Muslim man who joined the polytheists. We captured him. He, may Allah be pleased with him, asked: What did you do with him? They said: We killed him. He, may Allah be pleased with him, said: Why did you not put him in a house and then lock the door on him, that is, imprison him, and give him a little food daily, then ask him to repent three times, and if he repented, then fine, otherwise you would have killed him?! Then he, may Allah be pleased with him, said: O Allah! I am neither a witness over them nor did I order them, and when this matter reached me, I was not pleased with it.