They are those who are firm in regards to the fundamentals of the religion and its subsections, upon that which Allaah sent down and revealed upon his servant and Messenger Muhammad (sallallaahu alaihi wasallam). They are those establishing the call to that with all effort, sincerity and firm will. They are those carrying the knowledge of the Prophet (sallallaahu alaihi wasallam), expelling from it the distortions of those who have exaggerated (in its regard) and the undue claims of the people of falsehood and the interpretations of the ignorant ones.
They are those who are observant and lie in wait for every group that has deviated from the way of Islaam, like the Jahmees and the Mu'tazilees and the Khawaarij and the Rawaafidh and the Murji'ah and the Qadriyyah and all of those who have deviated from the way of Allaah and have followed their desires in every time and place - they not affected by the reproach of the blamers, in the cause of Allaah.They are the group that the Messenger of Allaah has praised and commended in his saying, "There will not cease to be a group from my Ummah manifest and upon the truth not being harmed by those who forsake them neither by those who oppose them until the hour is established." 
They are the Saved Sect firm upon that which the Messenger and his Companions were upon, those who have been distinguished and defined by the Messenger of Allaah when he mentioned that this Ummah shall divide into seventy three sects all going to the Hell-fire except one and it was said, "Who are they, O Messenger of Allaah?" He said, "They are those who are upon that which I and my Comapnions are upon."
And this is not something we say in exageration or a mere claim, but verily we speak a reality that the text of the Qur'aan and the Sunnah bears witness to, which history bears witness to, and to which their (i.e., the Ahlul-Hadeeth's) statements, their state of affairs, their writings and works also bear witness to. They are those who put before their eyes the statement of Allaah:
And hold fast, all of you together, to the rope of Allaah. 
And His statement:
And let those who oppose the Messengers commandment beware lest some fitnah befall them or a painful torment be inflicted on them. 
They are the most staunch in distancing themselves from opposing the command of the Messenger and the most distant from fitnah. They are those who make their constitution:
But no, by your Lord! They can have no faith, until they make you (O Muhammad (sallallaahu alaihi wasallam)) judge in all disputes between them, and find in themselves no resistance against your decisions, and accept them with full submission. 
They are those who give to the Qur'aan and the Sunnah their true worth and give it the honour and veneration it deserves, giving priority to them over all the statements of mankind, and give precedence to their guidance over the guidance of all the people, and they judge by them in all affairs with complete pleasure, with chests which are expanded and free of restraint or constriction, and they submit to Allaah and His Messenger (with) a complete submission in their 'aqeedah and their worship and their dealings. They are those concerning whom the statement of Allaah holds true:
The only saying of the faithful believers when they are called to Allaah and His Messenger (sallallaahu alaihi wasallam) to judge between them, is that they say, "We hear and we obey," and such are the prosperous ones.
They after all of the Comapanions - and at the head of them the rightly guided Caliphs - are the leaders of the taabi'een and at the head of them:
Sa'eed ibn al-Musayyib (d. 90H), 'Urwah ibn Zubair (d. 94H), 'Alee ibn al-Hussain Zain al-'Aabideen (d. 93H), Muhammad ibn Hanafiya (d. 80H), 'Ubaydullaah ibn 'Abdillaah ibn 'Utbah ibn Mas'ood (d. 94H or later), Saleem ibn 'Abdillaah ibn 'Umar (d. 106H), Qaasim ibn Muhammad ibn Abee Bakr as-Sadeeq (d. 106H), al-Hasan al-Basree (d. 110H), Muhammad ibn Sireen (d. 110H), 'Umar ibn 'Abdul-'Azeez (d. 101H) and Muhammad ibn Shihaab az-Zuhree (d. 125H).
Then the Atbaa'at-Taabi'een and at the head of them:
Imaam Maalik (d. 179H), al-Awzaa'ee (d. 157H), Sufiyaan ibn Sa'eed ath-Thawree (d. 161H), Sufyaan ibn Uyayna (d. 198H), Ismaa'eel ibn Ubya??? (d. 193H), Layth ibn Sa'd (d. 175H) and Aboo Haneefah an-Nu'maan (d. 150H).
Then those who followed them and at the head of them:
'Abdullaah ibn al-Mubaarak (d. 181H), Wakee' ibn al-Jarraah (d. 197H), the Imaam Muhammad ibn Idrees ash-Shaafi'ee (d. 204H), 'Abdur-Rahmaan ibn Mahdee (d. 198H), Yahya ibn Sa'eed al-Qataan (d. 198H) and Afaan ibn Muslim (d. 219H).
Then their students who followed them in this methodology, and at the head of them:
The Imaam Ahmad ibn Hanbal (d. 241H), Yahya ibn Ma'een (d. 233H) and 'Alee ibn al-Madeenee (d. 234H).
Then their students like al-Bukhaaree (d. 256H), Muslim (d. 261H), Abee Haatim (d. 277H), Abee Zara' (Aboo Zur'ah?) (d. 264H), Aboo Daawood (d. 275H), at-Tirmidhee (d. 279H) and an-Nasaa'ee (d. 303H).
Then those who proceeded in their way in the generations that preceded them, like Ibn Jareer (at-Tabaree?) (d. 310H), Ibn Khuzaymah (d. 311H), ad-Daaraqutnee (d. 385H) in his time, al-Khateeb al-Baghdaadee (d. 463H) and Ibn 'Abdul-Barr an-Niwaaree (d. 463H).
And 'Abdul-Ghanee al-Maqdasee (d. 620H), Ibn Salaah (d. 643H), Ibn Taymiyyah (d. 728H), al-Mizzee (d. 743H), adh-Dhahabee (d. 748H), Ibn Katheer (d. 774H) and their contemporaries who lived in their time and those who came after them, and followed their footsteps in holding on to the Book and the Sunnah up until the present day.
These are who I mean by Ahlul-Hadeeth.
 Hadeeth saheeh, collected by Muslim (3/1523), Ahmad (5/278-279), Aboo Dawood (3/4), Tirmidhee (4/420), Ibn Maajah (1/4-5), Haakim (4/449-450), at-Tabaraanee in Mu'jam al-Kabeer (7643) and Aboo Daawood at-Tayaalisi (p. 94, no. 689). Authenticated by al-Albaanee in As-Saheehah (270-1955).
Source: Makaanat Ahl ul-Hadith (trans. by Bilal Davies, forthcoming SP release)