The Noble Shaykh Muhammad Ibn Saalih al-Uthaimeen (Rahima-hu Allah) said:
Al-Firqah an-Naajiyah is the sect/group which adheres to that which the Prophet was upon in al-‘Aqeedah (creed, beliefs), al-‘Ibaadah (worship), al- Akhlaaq (character) and al-Mu’aamalah (business and social dealings with others). Shortcomings in these matters does not [necessarily] exclude someone frombeing of the ‘Saved Sect’. However, everyone will reach the degree which is
based upon his works.
Note that shortcomings/defects in the sphere of at-Tawheed could perhaps exclude someone from being of the ‘Saved Sect’. For exampl e defects in one’s Ikhlaas (doing something for the sake of Allah alone) [could take someone outside of the realm of the ‘Saved Sect’]. Similar is the case of one who falls into bid’ah (innovation), if the person engages in an innovation [Bid’ah Mukaffirah (a type of innovation which entails disbelief)] which excludes him from being among the ‘Saved Sect’.
The mention of al-Firqah an-Naajiyah came – with its description – in the Hadeeth which is authenticated from the Prophet: That the Jews divided into seventy-one (71) sects and the Christians divided into seventy-two (72) sects , and the Ummah (nation) of Muhammad [Ummah al-Ijaabah] will be divided into seventy-three (73) sects – and all of them would be in the Fire, except one (sect). When he was asked who they were, he said: ‘They are those who are upon that which I and my companions are upon today.’ In another narration, he said: [The saved group is] al-Jamaa’ah (i.e. those who unite together upon the Truth and do not divide themselves over it). [Reported by Abu Daawood, at-Tirmidhee, Ibn Maajah, Ibn Hibban, al-Haakim, Ahmad…and it is authentic. See: Silsilah al-Ahaadeeth as-Saheehah, vol. 1, pg. 402-414, Shaykh al-Albaanee]
The words: ‘…all of them would be in the Fire, except one (sect)… ’ do not necessitate that they remain in the Fire eternally (al-Khulood). Rather, the meaning is that their actions are such that justify them being admitted into the Fire (ad-Dukhool).
The words: ‘They are those who are upon that which I and my companions are upon today’ indicate that they are holding fast to the pure Islam which is absolutely free from any blemish or foreign influence.
[Quoted from: Majmoo’ Fataawa al -‘Aqeedah, Shaykh al-‘Uthaimeen, 1/38, 39 &
Sharh al-‘Aqeedah al-Waasitiyyah, al-‘Uthaimeen, 2/370-371]