Divine protection of Qur’an is a well established fact. This has been discussed in detail in my book "Aijazul Qur’an". Readers interested in this topic can refer to that book. Allah Ta'ala has categorically stated in the Qur'an:

إِنَّا نَحْنُ نَزَّلْنَا الذِّكْرَ وَإِنَّا لَهُ لَحَافِظُونَ

"We have, without doubts; sent down the message; and We will assuredly guard it (from corruption)." (15:9)

What does word Qur’an signify

Does the word Qur’an signify—words only, meaning only or both? In Nur-ul Anwar it is defined as:

هو (القران) اسم للنظم و المعنى جميعا

“Qur’an is the name given to both wording as well as meaning.”

It is obvious that when a speaker utters any sentence he gives equal preference to its words as well as meaning. There is a promise of divine protection of the Qur’an by Allah, this promise doesn't apply only to the word of the Qur’an but equally applies to its meaning also. We have discussed earlier that the best meaning Qur’an can have is the Hadith. Therefore, Hadith is also included in the promise of divine protection noted above.

Qur’anic measures for the protection of hadith

لَقَدْ كَانَ لَكُمْ فِي رَسُولِ اللَّهِ أُسْوَةٌ حَسَنَةٌ

"ye have indeed in the Messenger of Allah an excellent exemplar" (33:21)

وَمَا آتَاكُمُ الرَّسُولُ فَخُذُوهُ وَمَا نَهَاكُمْ عَنْهُ فَانْتَهُوا

"So take what the Messenger gives you, and refrain from what he prohibits you". (59:7)

مَنْ يُطِعِ الرَّسُولَ فَقَدْ أَطَاعَ اللَّهَ

"He who obeys the Messenger, obeys Allah".(4:80)

إِنْ كُنْتُمْ تُحِبُّونَ اللَّهَ فَاتَّبِعُونِي

"Say: If ye do love Allah, follow me: Allah will love you and forgive you your sins" (3:31)

In these and many other such verses, Qur’an exhorts its believers to know the life of Rasulullah (Sallallahu Alaihi Wasallam) and then follow it. Following of Sunnah was thus made obligatory by Qur’an. For this purpose the companions of Rasulullah (Sallallahu Alaihi Wasallam) took great pains to record whatever they saw and listened from Rasulullah (Sallallahu Alaihi Wasallam), this was rather the goal of their life.

First school at Sufa

Allah Ta’ala says in the Qur’an:

وَمَا كَانَ الْمُؤْمِنُونَ لِيَنْفِرُوا كَافَّةً فَلَوْلَا نَفَرَ مِنْ كُلِّ فِرْقَةٍ مِنْهُمْ طَائِفَةٌ لِيَتَفَقَّهُوا فِي الدِّينِ وَلِيُنْذِرُوا قَوْمَهُمْ إِذَا رَجَعُوا إِلَيْهِمْ لَعَلَّهُمْ يَحْذَرُونَ

"If a contingent from every expedition go forth to devote themselves to studies in religion, and admonish the people when they return to them, that thus they (may learn) to guard themselves (against evil). (9:122)

In early days of Islam, Muslims were busy in fighting their enemies at various fronts. It was likely that they would all engage themselves at the war-fronts and there would remain none to learn Hadith and as Allah Ta'ala wanted the Hadith and Sunnah to flourish and remain preserved, He commanded the Muslims that one group from amongst them should always remain with Rasulullah (Sallallahu Alaihi Wasallam) and learn Hadith and Sunnah, which constitutes essential part of Deen. Allah Ta’ala commanded Muslims that all of them should not go for war, one group should always stay back for learning. This we see in the form of school at Sufa. Sufa is a small platform in the grand mosque of Madinah, where Prophet (Sallallahu Alaihi Wasallam) used to teach Qur’an and Hadith. A group of devoted students always remained in Sufa. These students were not going out even for earning their livelihood lest they should miss the lessons from Rasulullah (Sallallahu Alaihi Wasallam). One of its famous students, Abu Hurairah (RA) describes how he was fainting with hunger but never left the company of Rasulullah (Sallallahu Alaihi Wasallam) at Sufa. These devoted students of Sufa are the people who took all pains to learn Hadith, they preserved it and passed it on to the next generation. These people took learning and teaching of Hadith as their whole time job. Rasulullah (Sallallahu Alaihi Wasallam) used to exhort these people for this job. He (Sallallahu Alaihi Wasallam) said:

نضّر الله إمرا أسمع مقالتي فودعها ثم أداها إلى من لم يسمعها

"May Allah bless him who listens from me Hadith, preserves it and then conveys it to those who have not listened." (Bukhari)

بلّغوا عنّي و لو آية

"Convey (to others) from me, even if it is a single statement"

فليغلغ الشاهد الغائب

"It is mandatory for those who are present should convey (my message) to those who are not present". (Bukhari)

To narrate Hadith is not an easy job

On one hand Rasulullah (Sallallahu Alaihi Wasallam) exhorted his companions to spread his message far and wide but at the same time he warned them to do this job very cautiously because of the delicacy of the matter. Rasulullah (Sallallahu Alaihi Wasallam) said:

من كذّب علي متعمدا فليتبوأ مقعده في النار

One who attributes a lie to me deliberately should find his abode in Hell. (Bukhari)

It was this Hadith which sent shock waves down the spine of the Sahaabah. Many Sahaabah never narrated any Hadith due to this fear, others who narrated thought hundred times first before narrating a Hadith. Hadhrat Hasan Bisri says:

هذا العلم دين فلينظروا عمن تأخذوا دينكم

"This knowledge is Deen, so scrutinise first from whom you are learning Deen."