If a Jew or Christian believes that Allah is One but does not rule according to the Quran
Question

If today there is a jew or a christian who believes in Alaah and that he has no partner. He believes in the prophethood of the Messenger of Allah . But he does not rule by the Quran even though he accepts it as being from Allah, but he deems it permissible to rule by the original torah. Is he a muslim. This needs a quick response if you can , for dawah purposes. Jazak Allahu Khair.
Praise be to Allah.We sent this question to our Shaykh ‘Abd al-Rahmaan al-Barraak, who replied as follows:
Among the basic principles of faith are Belief in all the Books that have been revealed from Allah, and belief in all the Messengers. These two principles include belief in the noblest of Books, which is the Quran, and the best of the Messengers, namely Muhammad (peace and blessings of Allah be upon him), the Seal of the Messengers and the Messenger of Allah to all of mankind from the time when Allah sent him until the time when the Hour will begin. Every person from every nation must believe in him and follow him and rule by his sharee’ah (laws). Whoever claims to believe in him and in the Quran, but does not rule according to it or follow him in everything that he brought and believe everything he told us, is not a Muslim or a believer. If he dies like this then he will be one of the people of Hell. If he claims to believe in Allah Alone, with no partner or associate, and in all the Messengers, belief in the Messenger and in the Quran does not only mean believing that they are true, without following them and ruling according to what they say. Many of the Mushrikeen believed in the Messenger of Allah (peace and blessings of Allah be upon him) in their hearts, and there were those who believed in him in their hearts and in the words they spoke, but this did not benefit them at all, like his uncle Abu Taalib. This belief did not help them at all when they insisted on not following. Similarly, the Jews and Christians who knew himas they knew their sons, and who admitted that they believed in the Messenger (peace and blessings of Allah be upon him), but this knowledge and belief did not benefit them at all when they refused to follow him. They were kaafirs and Allah decreed their blood and their wealth to be permissible for His Messenger (peace and blessings of Allah be upon him), so he fought them, and Allah caused him to prevail over them, and His religion to prevail over all other religions. Allah says (interpretation of the meaning):
“It is He Who has sent His Messenger (Muhammad (peace and blessings of Allah be upon him)) with guidance and the religion of truth (islam), to make it superior over all religions, even though the Mushrikoon (polytheists, pagans, idolaters, disbelievers in the Oneness of Allah) hate (it).” [al-Tawbah 9:33]
So every Jew and Christian has to enter the religion of Islam which Allah revealed to His Prophet Muhammad (peace and blessings of Allah be upon him), because the Message of Muhammad is the final Message, which abrogates the previous religions. Allah says (interpretation of the meaning):
“And whoever seeks a religion other than islam, it will never be accepted of him” [Aal ‘Imraan 3:85]
According to a saheeh hadeeth: “By the One in Whose hand is the soul of Muhammad, there is no one among this ummah, Jew or Christian, who hears of me than dies without believing in that with which I have been sent, but he will be one of the people of Hellfire.” (Reported by Muslim, 218).
On this basis, the religion of any Jew or Christian will not be correct unless he believes in the sharee’ah of Islam and adheres to the rulings of the Holy Quran. The Quran is Muhaymin (i.e., it testifies to the truth that is in the previous scriptures and exposes the falsehood that has been added to them), and it abrogates the previous Books. The Tawraat (Torah) and Injeel (Gospel) have been abrogated and have been changed and altered. And Allah knows best.