al-Haakim said:

Imam Ahmad ibn Hanbal did well when he commented on this report by saying that the victorious group who will prevail until the Hour begins is ashaab al-hadeeth (the people of hadeeth). Who is more deserving of this description than people who follow the way of the righteous and follow in the footsteps of the salaf who came before us, and exposed the falsehood of the people of bidah (innovation) by basing their arguments on the Sunnahs of the Messenger of Allaah (peace and blessings of Allaah be upon him)?

Marifat Uloom al-Hadeeth, by al-Haakim al-Nisaboori, p. 2, 3

2 al-Khateeb al-Baghdaadi said:

Allaah has made these people Ahl al-Hadeeth the pillars of shareeah, and He has destroyed through them all abhorrent innovations. They are the trustees of Allaah among His creation, the intermediaries between the Prophet (peace and blessings of Allaah be upon him) and his ummah. They are the ones who are striving hard to protect his religion; their light is shining, their virtues are well known, the signs of their sincerity are obvious, their way is prevailing, and their evidence is supreme. Every group has its own focal point which is based on whims and desires, apart from the people of hadeeth, whose reference point is the Quraan, whose evidence is the Sunnah and whose leader is the Messenger to whom they belong; they do not pay any attention to whims and desires, and they do not care about personal opinions. They are content with what is narrated from the Messenger, and they are the ones who are entrusted with it and they take care of it. They are the guardians and keepers of the faith, the vessels and bearers of knowledge.

If there is a difference of opinion concerning a hadeeth, people refer to them, and what they rule is what is accepted and listened to. Among them are prominent faqeehs, great imams, ascetics who are well-known among their tribes, men who are known for their virtue, skilled reciters of Quraan and good speakers. They are the majority and their way is the right way. Every innovator pretends to be following their path, and cannot dare to claim any other way. Whoever opposes them, Allaah will destroy him, and whoever goes against them, Allaah will humiliate him. They are not harmed by those who forsake them, and those who stay away from them will not prosper. The one who cares for his religion needs their help, the one who looks down on them is a loser, and Allaah is able to support them.

Sharf Ashaab al-Hadeeth, p. 15

Shaykh al-Islam Ibn Taymiyah said:

Hence it is clear that the people who most deserve to be called the victorious group are Ahl al-Hadeeth wal-Sunnah, who have no leader to follow blindly apart from the Messenger of Allaah (peace and blessings of Allaah be upon him). They are the most knowledgeable of people concerning his words and deeds, the most able to distinguish between what is sound and what is not [of hadeeth]. Their imams have deep knowledge of that, they are the ones who understand its meanings and are the most sincere in following it. They accept it and believe in it, and act upon it. They show love to those who adopt it and they show enmity to those who oppose it. They are the ones who measure any idea against that which is proven in the Quraan and Sunnah, so they never adopt any idea and make it one of the basic principles of their religion unless it is proven in that which the Messenger brought. Rather they make that which the Messenger brought, the Quraan and Sunnah, the foundation and basis of their beliefs. With regard to the issues concerning which people dispute, such as the attributes of Allaah, the divine decree, the threat of Hell, the names of Allaah and the principle of enjoining what is good and forbidding what is evil, etc., they refer that to Allaah and His Messenger. They examine the general ideas concerning which the different groups dispute, and whatever of these ideas is in accordance with the Quraan and Sunnah, they approve of it, and whatever goes against the Quraan and Sunnah, they reject it. They do not follow conjecture or whims and desires. For following conjecture is ignorance and following whims and desires without any guidance from Allaah is wrongdoing.

Majmoo al-Fataawa, 3/347, 348.

We should note that Ahl al-Hadeeth includes everyone who follows the hadeeth of the Prophet (peace and blessings of Allaah be upon him) and gives it precedence over all else, whether he is a scholar or an ordinary Muslim.

Shaykh al-Islam [Ibn Taymiyah] said:

We do not mean by Ahl al-Hadeeth only those who study it, write it down or narrate it, rather we mean anyone who takes care to memorize it, understand it and follow it, both inwardly and outwardly. The same may be said of Ahl al-Quraan (the people of the Quraan).

The basic quality of these people is their love of the Quraan and hadeeth, referring to them and their meanings, and acting upon what they learn.

Majmoo al-Fataawa, 4/95

The imams have said a great deal on this matter. You can learn more by referring to the sources quoted above, as well as volume 4 of Majmoo Fataawa Shaykh al-Islam Ibn Taymiyah.