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ʾinna lladhīna ʾāmanū thumma kafarū thumma ʾāmanū thumma kafarū thumma zdādū kufran lam yakuni llāhu li-yaghfira lahum wa-lā li-yahdiyahum sabīlan
As for those who believe and then disbelieve, then believe [again] and then disbelieve and then increase in disbelief, Allah shall never forgive them, nor shall He guide them to any way.
— Ali Quli Qarai
Surah An-Nisa', Verse 137
137. "Verily those who believed, then disbelieved, again believed, and again disbelieved, then increased in (their) disbelief, Allah will not forgive them, nor will He guide them to the (right) way."
Formerly a verse similar in meaning to this holy verse was detailed, saying that the repentance of such persons is not accepted and they are the real misguided ones. Also, Surah 'Ale-Imran, No.3 Verse 90 in this field says:
There are some people who change their features every day. This is either for the lack of research in Truth and religion, or it is a plot in order to weaken the belief of the believers. Surah 'Ale-Imran, No.3 Verse 72 also manifests this plan by stating that they believed at the opening of (the day, and disbelieved at the end of it, with the purpose that they might weaken the Muslims in their Faith. The clear example of the content of this verse is the persons such as Shabth-ibn-Rib'i whose instability can be, illustrated as follows:
He became Muslim but, after the death of the Prophet (S), he disbelieved. After that, he repented and joined to the adherents of Ali (as). Later, he changed to be the commander of Kharijites. Again he repented and went on to be as an adherent of Imam Hassan (as) and Imam Husayn (as). He wrote an invitation letter to Imam Husayn (as) but he showed his disloyalty to Muslim-ibn-' Aghil in Kufa (an-ancient city, in Mesopotamia). He accepted to be the commander of Yazid's troop in Karbala, and built a mosque in Kufa as a sign of gratitude for the slain of Imam Husayn (as). The verse says: