Musannaf Ibn Abi Shaybah 36096 — Reports on Tustar

The father of Muhammad bin Abd al-Rahman said: When the news of the conquest of Tustar reached Sayyiduna Umar (may Allah be pleased with him), he asked: "Did anything strange happen there?" He was told: "A Muslim apostatised and joined the polytheists, and we captured him." Sayyiduna Umar asked: "Then what did you do with him?" The people said: "We killed him." He said: "Why did you not keep him in confinement? You should have kept him confined for three days, given him one loaf of bread each day and called him to return to Islam. If he repented, well and good; otherwise you would have killed him." Then Sayyiduna Umar said: "O Allah, I was not present, I did not order it, and I was not pleased with it when it reached me."