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Islam is protected in totality till the day of judgement.
Allah, the almighty tells us in the Qur'an:
We have, Without doubt, sent down the message: and we will assuredly guard it (from corruption). (Qur'ân 15:9)
The promise made by Allah (the Most high) in Qur'an 15:9 is obviously fulfilled in the undisputed purity of the Qur'anic text throughout the fourteen centuries since its revelation. However, what is often forgotten by many Muslims is that the divine promise also includes, by necessity, the Sunnah of the Prophet (peace be upon him), because the Sunnah is the practical example of the implementation of the Qur'anic guidance, the wisdom taught to the Prophet

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along with the scripture, and neither the Qur'an nor the Sunnah can be understood correctly without the other.
Later, as the purity of the knowledge of the Sunnah became threatened, Allah (Ta'aalaa) caused the Muslim Ummah to produce individuals with exceptional memory skills and analytical expertise, who travelled tirelessly to collect thousands of narrations and distinguish the true words of prophetic wisdom from those corrupted by weak memories, from forgeries by unscrupulous liars, and from the statements of the large number of Ulama (scholars), the companions and those who followed their way. All of this was achieved through precise attention to the words narrated, and detailed familiarity with the biographies of the thousands of reporters of hadeeth.
The methodology of the expert scholars of hadeeth in assessing the narrations and sorting out the genuine from the mistaken and fabricated, forms the subject matter of the science of hadeeth.
Our islam is based on the Quran and the authentic Hadith.
It is important that we understand exactly the science of hadith, how they are preserved and their nature.
Articles About Hadith
The Science of Hadeeth
The Necessity of Adhering to the Sunnah
By Shaykh Muhammad Naasir-ud-Deen al-Albaanee (rahimahullah)