´'Abdullah bin Mas'ud narrated:` "We were in a tent with the Messenger of Allah (s.a.w), about forty of us when the Messenger of Allah (s.a.w) said to us: 'Would you be pleased to be a quarter of the people of Paradise?' They said:'Yes.' He said: 'Would you be pleased to be a third of the people of Paradise?' They said: 'Yes.' He said: 'Would you be pleased to be one half of the people of Paradise? Verily none shall enter Paradise except a Muslim soul. And you are not with relation to Shirk except like the white hair on the hide of a black bull or like the black hair on the hide of a red bull." Other chains report similar narrations.
Hadith Referenceسنن ترمذي / كتاب صفة الجنة عن رسول الله صلى الله عليه وسلم / 2547
It is narrated on the authority of 'Abdullah bin Mas'ud that the Messenger of Allah (ﷺ) (may peace and blessings be upon him) observed: Abusing a Muslim is an outrage and fighting against him is unbelief. Zubaid said: I asked Abu Wa'il: Did you hear it from 'Abdullah narrating if from the Messenger of Allah (ﷺ) (may peace and blessings be upon him)? He replied: Yes. But there is mention of the talk between Zubaid and Abu Wa'il in the hadith narrated by Shu'bah.
Shaykh Maulana Abdul Aziz Alvi
Hadith Commentary: Vocabulary of the Hadith: (1) Sabab: To abuse verbally, To find fault with someone’s honor and dignity.
(2) Al-Fisq: To go out, To depart, that is, to abandon truth and righteousness, To commit disobedience.
Source: Tuhfat al-Muslim: Commentary on Sahih Muslim, Page: 221