Mukhtasar Muslim

´Sayyiduna Usama bin Zaid (may Allah be pleased with him) says` The Messenger of Allah (peace and blessings be upon him) sent us on a military expedition. In the morning, we fought with the Harqat, who are from Juhainah. Then I found a man who said "La ilaha illallah" (There is no god but Allah), but I killed him with a spear. After that, I felt doubt in my heart (that it was not right to kill him after he said La ilaha illallah). I related this to the Messenger of Allah (peace and blessings be upon him), so he said, "Did he say La ilaha illallah and you killed him?" I said, "O Messenger of Allah! He said it out of fear of the weapon." The Prophet (peace and blessings be upon him) said, "Did you cut open his heart so that you would know whether his heart had said the word or not?" (Meaning, how could you know the state of his heart?) Then the Prophet (peace and blessings be upon him) kept repeating this until I wished that I had embraced Islam that day (so that after accepting Islam, I would not have been involved in such a sin, because previous sins of disbelief are forgiven upon embracing Islam). Sayyiduna Sa'd bin Abi Waqqas (may Allah be pleased with him) said, "By Allah, I will never kill any Muslim until the one with two bellies, i.e., Usama, kills him." A man said, "Has Allah not said: 'And fight them until there is no more fitnah (polytheism, idol worship) and the religion is Allah's alone'?" So Sayyiduna Sa'd (may Allah be pleased with him) said, "We fought (the disbelievers) so that there would be no fitnah, and you and your companions fight so that there is fitnah."