Question Summary:
how do we know hadiths are authentic and not corrupted because i have met people who do not believe in hadiths at all?

Question Detail:

how do we know hadiths are authentic and not corrupted because i have met people who do not believe in hadiths at all?

Answer :

In the name of Allah, Most Gracious, Most Merciful
Assalaamu `alaykum waRahmatullahi Wabarakatuh
In essence, “Hadith” refers to an act done, word spoken or a confirmation given by Rasulullah (sallallaahu alayhi wa sallam). “Hadith” has been accepted as a source of Islamic law, after the Quran. Its status has remained undisputed throughout the centuries aside from some individuals who have separated themselves from the mainstream of the Muslim population. Its authority is evident from the Quran. The Quran repeatedly reminds the believers to follow Rasulullah (sallallaahu alayhi wa sallam).
In order to fulfill the injunctions of the Quran, one is required to accept the authority Hadith. If one denies the authority of Hadith, it is impossible for him to fulfill and carry out the injunctions of the Quran, for example, we are commanded in the Quran to perform salat. But the Quran does not explain the methodology of salat. The Hadith explains to us the methodology of salat. If one had to rely simply on following the Quran, and not the hadith, he would not know the methodology of salat. Therefore, we are required to follow both, the Quran and Hadith. The Sahaba, Tabi’een and all the pious predecessors were staunch follows of Rasulullah (sallallaahu alayhi wa sallam)     
Hereunder are a few verses proving the authority of Hadith:
 
وَأَطِيعُوا اللَّهَ وَالرَّسُولَ لَعَلَّكُمْ تُرْحَمُونَ
“And obey Allah and the Messenger so that you may be shown mercy” (3:132)
 
وَمَنْ يُطِعِ اللَّهَ وَرَسُولَهُ يُدْخِلْهُ جَنَّاتٍ تَجْرِي مِنْ تَحْتِهَا الْأَنْهَارُ
“And whoever obeys Allah and his messenger, Allah shall admit him in the gardens underneath which rivers flow” (4:13)
                                                                                 
وَمَنْ يَعْصِ اللَّهَ وَرَسُولَهُ فَقَدْ ضَلَّ ضَلَالًا مُبِينًا
“And whoever disobeys Allah and His Messenger has gone astray into manifest error” (33:36) 
The Muhadditheen (experts in Hadith) have dedicated their lives in the various sciences of Hadith in order to preserve the authenticity of Ahadith. You may read more on the subject matter from a book “Authority of Sunnah” by Mufti Taqi Uthmani Saheb.
And Allah knows best
Wassalam
Ml. Talha Desai,
Student Darul Iftaa
Checked and Approved by:
Mufti Ebrahim Desai
Darul Iftaa, Madrassah In'aamiyyah