What is the refutation of the misconception, "Woe to Ammar! He will be killed by the transgressing group; he calls them to Paradise, and they call him to Hellfire," which some use to declare Mu'awiyah (may Allah be pleased with him) an infidel?

We must think well of the Companions, and whoever disparages them is a heretic. The fighting among the Companions was due to ijtihad (definition) (independent reasoning) and interpretation, and not due to an intention of falsehood. The instigators of this were the people of discord, and some of them regretted their fighting. The hadith (definition) "He will be killed by the transgressing group; he calls them to Paradise, and they call him to the Fire" indicates that the killers of Ammar were excused due to ijtihad, and that their calling to the Fire does not mean disbelief, but rather it is a warning, and it applies to the Khawarij.