How    can we tell the saheeh ahadith from the fabricated ones?
Question

I have a question regarding hadith. I know we should follow Muhammad's( ) example but how sure are we that some of the hadith we have today are not corrupt and changed. I am by no means judging the hadith and saying they are wrong. please understand that. it's just that some muslims have told me alot of hadith is changed and bogus. I follow the hadith to the best of my ability. Please help me with any knowledge. thank you.
Praise be to Allah.Allah has guaranteed to protect His religion, which includes preserving His miraculous Book, and preserving the Sunnah of His Prophet which helps us to understand the Quran. Allah says (interpretation of the meaning):
Verily, We, it is We Who have sent down the Dhikr (i.e. the Quran) and surely, We will guard it (from corruption). [Al-Hijr 15:9]
The word Dhikr here includes both the Quran and the Sunnah.
Many people in the past and at present have tried to insert weak and fabricated ahadith into the pure shareeah and the Prophetic Sunnah. But Allah has thrown their plots back in their faces and has provided means of protecting His religion. Among these means are the trustworthy and reliable scholars who sifted through the reports and checked their sources, examining the biographies of the narrators and even describing the point at which a narrator began to be confused in his narration, and stating who narrated from him before he became confused and who narrated from him afterwards. They described the journeys of the narrator, which cities he visited and from whom in each city he took reports. They checked many details about each narrator, more than can be listed here. All of this indicates that the religion of this Ummah is protected, no matter how hard our enemies try to plot and play about with the religion and distort it.
Sufyaan al-Thawri said: the angels are the guardians of the heavens and the scholars of hadith are the guardians of this world.
Al-Haafiz al-Dhahabi mentioned that Haaroon al-Rasheed was about to execute a zindeeq (heretic), and the zindeeq said: What are you going to do about the one thousand ahadith I have fabricated? Al-Rasheed said: What are you going to do, O enemy of Allah, about Abu Ishaaq al-Fazaari and Abd-Allah ibn al-Mubaarak, who will sift through those ahadith and examine them letter by letter?
The seeker of knowledge can find out about the fabricated (mawdoo) and weak (daeef) ahadith very easily, by looking at the isnaads or chains of narrators, and finding out about the people mentioned there in the books of men i.e., narrators (kutub al-rijaal) and the books which state which narrators are sound or otherwise (kutab al-jarh wal-tadeel).
Many scholars have compiled these fabricated and weak ahadith in books devoted solely to these type of reports, so that it is easy to find out about them then one can beware of them and warn others about them. These books include al-Ilal al-Mutanaahiyah by Ibn al-Jawzi, al-Manaar al-Muneef by Ibn al-Qayyim, al-Laaali al-Masnooah fil-Ahadith al-Mawdooah by al-Suyooti, al-Fawaaid al-Majmooah by al-Shawkaani, al-Asraar al-Marfooah fil-Ahadith al-Mawdooah by Ibn Arraaq, and Daeef al-Jaami al-Sagheer and Silsilat al-Ahadith al-Daeefah wal-Mawdooah, both by Shaykh al-Albani, may Allah have mercy on him.
The fact that the brother has heard about weak and fabricated ahadith indicates that he is making the distinction praise be to Allah between what is saheeh and what is not. This is by the grace of Allah, and is a sign that Allah is protecting this shareeah, as we mentioned above.
We advise our brother to read the books of men i.e., narrators (kutub al-rijaal), the books which state which narrators are sound or otherwise (kutab al-jarh wal-tadeel) and the books of the science of hadith (kutub mustalah al-hadith), so that he can learn the extent of the efforts made by the scholars in the service of the Sunnah.
And Allah is the source of strength.