Sayyiduna Abu Bakrah (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) passed by a man who was in prostration as he was going to the prayer. He performed the prayer, and when he passed by him on his way back, the man was still in prostration. The Prophet (peace and blessings be upon him) stood up and said: "Who will kill this man?" A man stood up, rolled up his sleeves, drew his sword, brandished it and said: "O Prophet of Allah, may my father and mother be sacrificed for you! How can I kill a man who is in prostration and who bears witness that there is no god but Allah and that Muhammad (peace and blessings be upon him) is His servant and His Messenger?" Then the Prophet (peace and blessings be upon him) said: "Who will kill this man?" Another man stood up and said: "I will." He rolled up his sleeves, drew his sword and brandished it, but then his hand began to tremble. He said: "O Prophet of Allah, how can I kill a man who is in prostration and who bears witness that there is no god but Allah and that Muhammad (peace and blessings be upon him) is His servant and His Messenger?" The Prophet (peace and blessings be upon him) said: "By the One in whose hand is the soul of Muhammad, had you killed him, it would have been the first trial (fitnah) and the last."
Ahmad recorded it, and al-Tabarani recorded it without a satisfactory account. The narrators of Ahmad are the narrators of the Sahih.