Sinner Not a Believer When Actively Committing the Sin

 بِسۡمِ اللّٰہِ الرَّحۡمٰنِ الرَّحِیۡمِ

‌قُدُّوسٌ ‌قُدُّوسٌ ‌قُدُّوسٌ

الصلاة والسلام عليك يا سيدي يا رسول الله

In the Name of Allah, the Rahman, the Merciful

Holy, Holy, Holy

The issue of the reality of Faith caused much differing in the early days of Islam. Several schismatic groups emerged, breaking from the main Jama’ah of the Muslims, meaning Ahl us-Sunnah, on the question of Faith and its relation to deeds. The Kharijites, Murji’ites and Mu’tazilites have all dissented from the Sunnah and orthodoxy on the question of Faith. The Kharijites say that the committing of mortal sin expels a Muslim from Islam, while the Murji’ites were on the opposite end of the spectrum when they said that sins have absolutely no consequence upon a Muslim’s Faith. The Mu’tazilites also dissented on this question, when Wasil bin Ata broke from the circle of al-Hasan al-Basri رضى الله عنه and invented the doctrine of al-Manzilah bain al-Manzilatain, meaning when a Muslim commits a mortal sin he enters a state between the two states of being a Mu’min (believer) and of being a Kafir (unbeliever). This intermediate state, according to the Mu’tazilah, is therefore neither described as Islam or Kufr. Like the Kharijites, the Mu’tazilites and those sects under their influence such as the Shi’ites, believe that sinners will be made to enter Hell and remain there eternally. But the Holy Prophet Muhammad صلى الله عليه وآله وسلم said:

لاَ يَزْنِي الزَّانِي حِينَ يَزْنِي وَهْوَ مُؤْمِنٌ وَلاَ يَسْرِقُ حِينَ يَسْرِقُ وَهْوَ مُؤْمِنٌ وَلاَ يَشْرَبُ حِينَ يَشْرَبُهَا وَهْوَ مُؤْمِنٌ وَالتَّوْبَةُ مَعْرُوضَةٌ بَعْدُ

A fornicator is not a believer when he is fornicating, nor is a thief a believer when he is stealing, nor is a drunk a believer when he is drinking. But repentance is placed thereafter (Sahih al-Bukhari & Sahih Muslim)

Only at the time a sinner is committing a major sin, such as fornication, theft or intoxication, he is not a believer. But that is only true for the duration in which he is committing the major sin, as made clear in another Hadith:

إِذَا زَنَى الرَّجُلُ خَرَجَ مِنْهُ الإِيمَانُ كَانَ عَلَيْهِ كَالظُّلَّةِ فَإِذَا انْقَطَعَ رَجَعَ إِلَيْهِ الإِيمَانُ

When a man commits fornication, Faith departs from him and is over him like a cloud. So when he ceases, Faith returns to him (Sunan Abi Dawud)

This means that even without active repentance, a sinner is still considered a Believer. Faith automatically returns to him when is has concluded the commission of the cardinal sin.