Who are Ahlu Sunnah? (Noorul Ulama M.A.Usthad)

" Rasulullah ('alaihi 's-salam) declared, while telling about what will happen to his umma in future:  
“The Sons of Israil parted into 72 nations. And my umma will part into 73 groups. Of them, only one will be saved, and all others will go to Hell.”
 As-Sahabat al-kiram upon hearing this, asked, 'Oh Rasul-Allah! Which is that?' He declared, 'They are those who follow my and my Sahaba's path.'
This hadith ash-Sharif was reported from 'Abdullah  ibn 'Umar (radi-Allahu 'anh).
As reported from Muawiya (radi-Allahu 'anh) 
by Imam Ahmad and Abu Dawud, Rasulullah ('alaihi 's-salam) declared, 'Of them, 72 are in Hell, and the remaining one is in Paradise. And this is one jamaat.'
This hadith ash-Sharif is also quoted in the chapter on 'I'tisam' of the book Mishkat.
 Oh Muslims! We must search and find this single community of salvation mentioned in this hadith and their beliefs which cause entrance to Paradise and should beware of heretical groups who oppose these beliefs! In this way, we shall endeavor to get saved from the Hell fire and flame!
Hadrat Ghawth al-azam 'Abd al-Qadir al-Geilani (QS)explained the former hadith and the word 'jamaat' in the latter hadith in these words: 'The believer (Mumin) should adapt himself to the Sunnat and to the Jamaat. The Sunnat is the way shown by Rasulullah ('alaihi 's-salam). The Jamaat is composed of the things done unanimously by as-Sahabat al-kiram who lived in the time of the four caliphs called Khulafa' ar-rashidin. A Muslim must prevent the multiplication of the men of bidat and be away from them and should not greet them. Ahmad Ibn Hanbal, the imam of our madhhab, said that greeting a man of bidat meant loving him since it had been declared in a hadith ash-Sharif, "Disseminate [your] greeting (salam)! Love one another in this way!" ' These are written on the 90th page of Gunyat at-talibin.
Great alim Ahmad ibn Hajar al-Haitami(rah), the last muhaqqiq, wrote on this subject in detail on page 149 of his work Sawa'iq al-muhriqa, where he said, 'Those who dissent from the Ahl as-Sunnat faith are called mubtadi'. They began to come forth in the first century [of Islam].'
"Hadrat Ibn Hajar al-Haitami said in his work Fat'h al-jawad, 'Mubtadi' is the person who does not have the faith (itiqad) conveyed unanimously by Ahl as-Sunnat. This unanimity was transmitted by the two great imams Abu 'l-Hasan al-Ashari and Abu Mansur al-Maturidi and the 'alims who followed their path.' On the 205th page of the book Al-fatawa al-hadithiyya, it is written, 'Man of bidat means one whose beliefs are different from the Ahl as-Sunnat faith. The Ahl as-Sunnat faith is the faith of Abu 'l-Hasan al-Ashari, Abu Mansur al-Maturidi and those who followed them. One who brings forth something which is not approved by Islam becomes a man of bidat.'
 
Shafi'i alim Ahmad Shihab ad-din Kalyubi al-Misri (Rah)wrote on the fourth volume of his marginalia to the book Kanz ar-raghibin: 

'One who departs from what Abu 'l-Hasan al-Ashari(RA) and Abu Mansur al-Maturidi (RA) reported is not Sunni. These two imams followed the footprints of Rasulullah (SallallahuAlaihiwasallam) and his Sahaba(RA).'

[Shaykh Abu Ahmed AbdulQadir Malibari(Noorul Ulama M.A.Usthad)]