Qur’anic proof of bara from false Imams
We read in Surah Al-Baqarah verse 166/167:
إِذْ تَبَرَّأَ ٱلَّذِينَ ٱتُّبِعُوا۟ مِنَ ٱلَّذِينَ ٱتَّبَعُوا۟ وَرَأَوُا۟ ٱلْعَذَابَ وَتَقَطَّعَتْ بِهِمُ ٱلْأَسْبَاب
[And they should consider that] when those who have been followed disassociate themselves from those who followed [them], and they [all] see the punishment, and cut off from them are the ties [of relationship],
وَقَالَ ٱلَّذِينَ ٱتَّبَعُوا۟ لَوْ أَنَّ لَنَا كَرَّةً فَنَتَبَرَّأَ مِنْهُمْ كَمَا تَبَرَّءُوا۟ مِنَّا ۗ كَذَٰلِكَ يُرِيهِمُ ٱللَّهُ أَعْمَٰلَهُمْ حَسَرَٰتٍ عَلَيْهِمْ ۖ وَمَا هُم بِخَٰرِجِينَ مِنَ ٱلنَّارِ
Those who followed will say, "If only we had another turn [at worldly life] so we could disassociate ourselves from them as they have disassociated themselves from us." Thus will Allah show them their deeds as regrets upon them. And they are never to emerge from the Fire.
We can see from these verses that those which follow false Imams in this world will face destruction in the next one. When the truth reaches them, it will be too late, at that point the false Imams will regret their actions and do dissociation (Tabarra) on their adherents and their adherents will to Tabarra on them as they had clung to then on earth assuming they would act as a source of guidance and salvation for them.
Clearly we can gauge from this verse that Tabarra is not an unIslamic practice. That Allah (swt) clearly cites this in the Qur’an evidences the fact that dissociating oneself from unjust imams is pursuant to the Qur'an. If the people destined for Hellfire will practice Tabarra when it's too late, is it not right we disassociate ourselves from unjust Imams now, before it is too late?
We read in Surah Qasas verse 63:
قَالَ ٱلَّذِينَ حَقَّ عَلَيْهِمُ ٱلْقَوْلُ رَبَّنَا هَٰٓؤُلَآءِ ٱلَّذِينَ أَغْوَيْنَآ أَغْوَيْنَٰهُمْ كَمَا غَوَيْنَا ۖ تَبَرَّأْنَآ إِلَيْكَ ۖ مَا كَانُوٓا۟ إِيَّانَا يَعْبُدُونَ
Those upon whom the word will have come into effect will say, "Our Lord, these are the ones we led to error. We led them to error just as we were in error. We declare our disassociation [from them] to You. They did not used to worship us."
In the same way these people will on the Day of Judgment disassociate themselves from charlatan imams the Shia do likewise and take the Imams of the Ahul’lbayt whom Messenger of Allah (s) described as his Caliphs & whose obedience is a part of one’s faith.
The Shias are those who in this world have concluded the Imams of Ahlubayt (as) represent truth and dissociate from their enemies, rather than equivocate with regard to their enemies – a practice which jeopardises their eternal souls in the afterlife. Often such persons worthy of Tabarra were distanced by the Holy Prophet (s) himself during his own lifetime.
Quranic proof of cursing deviants
We read in Surah Hud verse 18 Allah swt says :
لَعْنَةُ ٱللَّهِ عَلَى ٱلظَّٰلِمِينَ
(the curse of Allah is upon the wrongdoers.)
In Surah Aal-e-Imran verse 61, Allah (swt) states:
لَّعْنَتَ ٱللَّهِ عَلَى ٱلْكَٰذِبِينَ
(curse of Allah upon the liars)
If it is argued that this right of cursing belongs exclusively to Allah (swt) as per the above two examples. We shall point out that Allah (swt) says as follows in Surah Aal-e-Imran verse 87:
أُو۟لَٰٓئِكَ جَزَآؤُهُمْ أَنَّ عَلَيْهِمْ لَعْنَةَ ٱللَّهِ وَٱلْمَلَٰٓئِكَةِ وَٱلنَّاسِ أَجْمَعِينَ
Those - their recompense will be that upon them is the curse of Allah and the angels and the people, all together,
We read in Surah Al-Baqarah verse 161:
إِنَّ ٱلَّذِينَ كَفَرُوا۟ وَمَاتُوا۟ وَهُمْ كُفَّارٌ أُو۟لَٰٓئِكَ عَلَيْهِمْ لَعْنَةُ ٱللَّهِ وَٱلْمَلَٰٓئِكَةِ وَٱلنَّاسِ أَجْمَعِينَ
Indeed, those who disbelieve and die while they are disbelievers - upon them will be the curse of Allah and of the angels and the people, all together,
Both verses evidence the fact that deviated people are cursed by Allah, His Angels, and people (in general).
We read in Surah Al-Baqarah verse 159:
إِنَّ ٱلَّذِينَ يَكْتُمُونَ مَآ أَنزَلْنَا مِنَ ٱلْبَيِّنَٰتِ وَٱلْهُدَىٰ مِنۢ بَعْدِ مَا بَيَّنَّٰهُ لِلنَّاسِ فِى ٱلْكِتَٰبِ ۙ أُو۟لَٰٓئِكَ يَلْعَنُهُمُ ٱللَّهُ وَيَلْعَنُهُمُ ٱللَّٰعِنُونَ
Indeed, those who conceal what We sent down of clear proofs and guidance after We made it clear for the people in the Scripture - those are cursed by All
We read in Surah Nisa verse 93:
وَمَن يَقْتُلْ مُؤْمِنًا مُّتَعَمِّدًا فَجَزَآؤُهُۥ جَهَنَّمُ خَٰلِدًا فِيهَا وَغَضِبَ ٱللَّهُ عَلَيْهِ وَلَعَنَهُۥ وَأَعَدَّ لَهُۥ عَذَابًا عَظِيمًا
But whoever kills a believer intentionally - his recompense is Hell, wherein he will abide eternally, and Allah has become angry with him and has cursed him and has prepared for him a great punishment
We read in Surah Al-Ahzab verse 57:
إِنَّ ٱلَّذِينَ يُؤْذُونَ ٱللَّهَ وَرَسُولَهُۥ لَعَنَهُمُ ٱللَّهُ فِى ٱلدُّنْيَا وَٱلْءَاخِرَةِ وَأَعَدَّ لَهُمْ عَذَابًا مُّهِينًا
Indeed, those who abuse Allah and His Messenger - Allah has cursed them in this world and the Hereafter and prepared for them a humiliating punishment.