Mocking the Prophet Muhammad (peace be upon him) is explicit and clear disbelief. Allah, the Exalted, said: (And if you ask them, they will surely say, "We were only conversing and playing.") Say, "Is it Allah and His verses and His Messenger that you were mocking?" [At-Tawbah: 65]. Whoever insults the Prophet Muhammad (peace be upon him) if he is a Muslim is an apostate, and he must be killed as a punishment if he does not repent, according to consensus. Al-Qadi Iyad said: "The Ummah has unanimously agreed on killing anyone who belittles the Prophet from among the Muslims and insults him." Ibn al-Mundhir said: "The common people of knowledge have agreed that whoever insults the Prophet Muhammad (peace be upon him) is to be killed." Among the evidence for this is His saying, the Exalted: (Indeed, those who harm Allah and His Messenger, Allah has cursed them in this world and the Hereafter and prepared for them a humiliating punishment... Cursed are they wherever they are found, seized and massacred.) [Al-Ahzab: 57-61]. These verses indicate his disbelief and the necessity of killing him. And the Prophet (peace be upon him) said: "O assembly of Muslims, who will excuse me from a man who has harmed me regarding my family? By Allah, I have only known good about my family... Then Sa'd ibn Mu'adh stood up and said: 'I, O Messenger of Allah, will excuse you. If he is from the Aws, I will strike his neck, and if he is from our brothers from the Khazraj, command us, and we will do your command..." This is in Sahih al-Bukhari 4: 1517. Sa'd ibn Mu'adh's statement (may Allah be pleased with him) is evidence that killing those who harm the Prophet (peace be upon him) was known to them, and the Prophet (peace be upon him) approved it and did not deny it, nor did he say to him that it is not permissible to kill him. And from Ibn Abbas (may Allah be pleased with him): "There was a blind man whose mother was a slave who used to insult the Prophet (peace be upon him) and speak ill of him. He would forbid her, but she would not stop, and he would admonish her, but she would not listen. One night, she began to insult the Prophet (peace be upon him) and curse him, so he took a dagger and placed it in her belly and leaned on it until he killed her. A child fell between her legs and stained the area with blood. When morning came, he mentioned this to the Prophet (peace be upon him), who gathered the people and said: 'I ask Allah for a man who did what he did to come forward, for he has a right over me.' The blind man stood up, stepping over the people, trembling until he sat before the Prophet (peace be upon him) and said: 'O Messenger of Allah, I am her owner. She used to insult you and speak ill of you. I would forbid her, but she would not stop, and I would admonish her, but she would not listen. I had two sons with her like two pearls, and she was a companion to me. When last night she began to insult you and speak ill of you, I took the dagger and placed it in her belly and leaned on it until I killed her.' The Prophet (peace be upon him) said: 'Bear witness that her blood is nullified.'" This is in Sunan Abi Dawood 2: 533, Al-Mustadrak 4: 394, Sunan Al-Daraqutni 3: 112, Al-Mu'jam Al-Kabir 11: 351, Sunan Al-Bayhaqi Al-Kabir 7: 60, and Tafsir Al-Qurtubi 8: 76. Because the apostate's killing is established by consensus and corroborating texts, including the saying of the Prophet (peace be upon him): "Whoever changes his religion, kill him," in Al-Muwatta 3: 324, and Sahih al-Bukhari 6: 2537. The one who insults is an apostate who has changed his religion, as stated in Tanbih Al-Wulat 1: 294-296. However, if he repents afterward, his repentance is accepted; the majority of scholars agree on accepting the repentance of the apostate and averting the killing from him by Islam. The reason for killing the one who insults the Prophet (peace be upon him) is disbelief, not specifically the insult, as the insult is a specific form of disbelief that falls under the general rule: "Whoever changes his religion, kill him." The meaning of "kill him" is as long as he is changing his religion; if he converts to Islam, the reason for killing is removed.