How can one reconcile the Hadith in which the Messenger of Allah (peace be upon him) forbade the killing of anyone who testifies that there is no god but Allah and that Muhammad is the Messenger of Allah, and who performs the prayer, with the Hadith: "I have been commanded to fight the people until they say: 'There is no god but Allah.' So whoever says: 'There is no god but Allah,' then he has protected his wealth and his life from me, except by its right, and his reckoning is with Allah," which Abu Bakr Al-Siddiq (may Allah be pleased with him) used as evidence to fight those who differentiated between prayer and zakat?

There is no contradiction between the hadiths regarding the killing of a Muslim. The prohibition of killing applies to a Muslim who outwardly demonstrates commitment to Islam and has not committed an act that warrants killing. Killing, on the other hand, applies to one who has done something that necessitates fighting them, such as refusing to pay Zakat. The Prophet, peace and blessings be upon him, clarified what invalidates the sanctity of blood through his saying: «The blood of a Muslim who testifies that there is no god but Allah and that I am the Messenger of Allah is not lawful except in one of three cases: the married fornicator, a life for a life, and one who abandons his religion and separates from the community.» His saying: «I have been commanded to fight the people until they say: There is no god but Allah. So whoever says: There is no god but Allah, has protected his wealth and his life from me, except by its right,» does not contradict this, for "except by its right" includes everything that invalidates the sanctity of life and wealth, as Abu Bakr Al-Siddiq did when fighting those who withheld Zakat. As for the hypocrites, the Prophet, peace and blessings be upon him, did not punish them due to the lack of legally established proof of their disbelief, or for fear of a greater fitna (discord). This ruling remains valid to this day.