Is it forbidden to abandon the Hadith and act solely upon the Qur’an, as a guarantee and reliability, for fear of forgetfulness or fabrication by some narrators?

It is not permissible to act upon the Quran without the Sunnah (sayings and actions) of the Messenger of Allah, peace and blessings be upon him. Whoever does so has not truly adhered to the Quran, because it is the Quran itself that commanded adherence to the Sunnah, as Allah the Almighty said: "And whatever the Messenger has given you - take it; and whatever he has forbidden you - refrain from it." [Al-Hashr: 7]. The claim that the reason for abandoning the Sunnah is fear of falsehood or forgetfulness is a baseless assertion; for the Prophetic Sunnah is preserved just as the Quran is preserved, and scholars have distinguished its authentic parts from its weak ones.