How is the hadith "Ammar will be killed by the transgressing group" understood in light of Lady Aisha's support for Muawiya, and how is it permissible for Muslims to fight each other when there are those among them who were promised Paradise, especially since "If two Muslims meet with their swords, then both the killer and the killed are in Hellfire"?

A'ishah (may Allah be pleased with her) did not go out to fight Ali and Mu'awiyah. Rather, she went out with Talhah and Az-Zubayr to pursue the killers of Uthman and to demand that Ali punish them. Her objective was to reconcile the Muslims, which led to the Battle of the Camel.

Regarding the Hadith of Ammar, Shaykh Al-Islam Ibn Taymiyyah explained that the Muslims split into two factions: one with Ali and one with Mu'awiyah. What occurred was exactly as the Prophet (peace be upon him) foretold, for it is authentically narrated that Allah would reconcile through his son Al-Hasan two great factions of Muslims. The Prophet (peace be upon him) praised Al-Hasan for this reconciliation. This text indicates that what Al-Hasan did was commendable and pleasing to Allah and His Messenger, and that the fighting was not ordained by Allah and His Messenger.

This clarifies that those killed at Siffin were not like the renegade Kharijites whose fighting was commanded. Instead, reconciliation between them was praised. This is why the Companions and Imams agreed on fighting the renegade Kharijites, whereas no narration from the Prophet (peace be upon him) speaks of fighting the Companions. Rather, he showed sadness, wished it would not happen, thanked some Companions, acquitted both parties of disbelief and hypocrisy, and permitted prayers for mercy upon the dead of both factions.

The Qur'an testified that the fighting between believers does not remove them from faith, by Allah's saying: ﴿وَإِن طَائِفَتَانِ مِنَ الْمُؤْمِنِينَ اقْتَتَلُوا فَأَصْلِحُوا بَيْنَهُمَا ۖ فَإِن بَغَتْ إِحْدَاهُمَا عَلَى الْأُخْرَىٰ فَقَاتِلُوا الَّتِي تَبْغِي حَتَّىٰ تَفِيءَ إِلَىٰ أَمْرِ اللَّهِ ۚ فَإِن فَاءَتْ فَأَصْلِحُوا بَيْنَهُمَا بِالْعَدْلِ وَأَقْسِطُوا ۖ إِنَّ اللَّهَ يُحِبُّ الْمُقْسِطِينَ﴾ [Al-Hujurat: 9] (And if two factions among the believers should fight, then make settlement between them. But if one of them oppresses the other, then fight against the one that oppresses until it returns to the ordinance of Allah. And if it returns, then make settlement between them in justice and act equitably. Indeed, Allah loves those who act equitably). So, He called them believers and brethren despite the fighting and oppression.

As for the mentioned Hadith, "If two caliphs fight, then one of them is cursed," it is a fabricated lie.

Mu'awiyah did not claim the Caliphate, nor was he sworn allegiance to it when he fought Ali. Rather, Ali saw it obligatory to obey and pledge allegiance to him, while Mu'awiyah and his companions believed that it was not obligatory for them as long as Uthman's killers were present in Ali's army, and they thought that Ali could not repel them.

Allah acquitted Ali and Uthman of what some ignorant people assumed about them.

As for Ammar's Hadith, "He will be killed by the transgressing faction," there is nothing in it that contradicts what has been mentioned, because Allah Almighty called both factions believers and brethren despite the presence of fighting and transgression. Not every transgression, injustice, or aggression removes people from faith or necessitates their cursing. The sincere Mujtahid (one who strives to form an independent judgment) who errs is forgiven for his error.

Transgressors who are sincere in their interpretations are fought to repel the harm of their transgression, not as punishment for them. They remain just and are not considered corrupt.

The Hadith of Ammar is not explicit that the term applies to Mu'awiyah and his companions. Rather, it could refer to the group that killed him, and whoever approved of his killing would be judged like them.

Among the army were those who did not approve of Ammar's killing, even Mu'awiyah and Amr. Mu'awiyah interpreted it by saying that the one who brought him was the one who killed him, not his fighters, and Ali refuted this interpretation.

In summary, the Companions are believers and Muslims, and Ali ibn Abi Talib and those with him were more entitled to the truth.