Is it not possible that the companions erred or the hypocrites of Madina fabricated Hadith?

It is true that all the companions were noble, in-fact they were the best of men/women. But isn't it possible for them to forget or make human errors in relating the ahaadith? So, why don't we have Jarh wa Ta'deel among the sahaba?

This was an issue for me in the early days, and I had asked some mashaykh but their answer did not satisfy me. This remained until I asked shaikh Umar al Muqbil, may Allah bless him, whose answer to me has been summarized below:

This is a valid question due to the fact that Allah said: "Among you are some who desire this world, and among you are some who desire the Hereafter." (Aale Imraan 3:152)

It is well known that hypocrites were hidden in Madinah, so how would we know that the man who narrated the hadith was a believer or not?

And this is often brought up by Hadith rejectors and non-Muslim researchers in general. And furthermore, as you mentioned, it was possible for them to make errors like other humans. But this can be answered in the following ways:

1. Name us one companion who narrated a hadith yet we don't have his biography. Through his biography, we know what he did and how he lived, whether he participated in Jihad or not, and so on.
2. If a hypocrite was to narrate, Allah would expose his hypocrisy, since he promised to preserve this religion.
3. The companions had such a level of faith that they would not speak without certainty, and we have narrations proving how they would travel a journey of a month to another companion just to confirm one narration.

Then, shaikh went onto what books should be studied for hadith studies:

1. Sharh at-Tadhkirah of Ibn Mulaqqin.
2. Nuzhatun-Nazr sharh Nukhbat-ul Fikr of Ibn Hajr.
3. Taqreeb Nuzhatun-Nazr (of any).
4. Tadreeb ar-Raawi of as-Suyuti.
5. Taqreeb at-Tahdheeb of Ibn Hajr.

So, how about studying Muqaddimah of Ibn Salah and Bayqooniyyah?

These two books are for the laymen to get a general idea and an overview of the science of Hadith, but a student of knowledge can always begin with the arrangement mentioned above.