How do we make sure if a Hadith is sahih or fake?

To determine whether a hadith is sahih (authentic) or fake, scholars rely on several criteria, including the chain of narrators (isnad), the integrity of the narrators, and the consistency of the content with the Qur'an and established teachings of Islam.

For instance, Al-Kafi explains that when assessing a hadith, one should consider its alignment with the Holy Qur'an. The Imam said, If you find a Hadith with evidence in the Holy Quran to support it or a Hadith of the Messenger of Allah (you may follow it). Otherwise, you follow the one that has come to you through the trustworthy narrator. Al-Kafi 22:200. This highlights the importance of the Qur'an as a reference point for validating hadith.

Additionally, a narration from the Prophet ﷺ emphasizes this principle. He stated, O people, whatever comes to you in the form of my Hadith, if it agrees with the Holy Book of Allah, it is genuine, but whatever comes to you that does not agree with the book of Allah you must know that I have not said it. Al-Kafi 22:203. This reinforces the necessity of ensuring that reported sayings do not contradict the teachings of the Qur'an.

In summary, the authenticity of a hadith is confirmed by its compatibility with the Qur'an, the reliability of its narrators, and thorough scholarly investigation into its chain and content.