How does one respond to those who permit cursing Mu'awiyah ibn Abi Sufyan, citing a historical narration indicating that he was a "bribetaker," and claim that this justifies cursing him and necessitates rejecting the hadiths he narrated?

The narration does not mention a bribe; rather, Ibn Umar accepted money from Mu'awiyah, but he did not pledge allegiance to Yazid during Mu'awiyah's lifetime because he did not believe in the legitimacy of pledging allegiance to two caliphs. Ibn Umar pledged allegiance to Yazid after Mu'awiyah's death and after people had gathered around him, citing the hadith, "A banner will be erected for every traitor on the Day of Resurrection." Even if it is conceded that the money was a bribe, this does not mean cursing Mu'awiyah, for cursing is a punishment for those whom deterrents such as repentance and effacing good deeds have not averted. Furthermore, committing a major sin does not invalidate a narration unless it impugns the narrator's truthfulness. In any case, the Ahl al-Sunnah do not consider Mu'awiyah or anyone else infallible from sins, for sins are expiated by causes such as repentance, seeking forgiveness, and effacing good deeds, and this applies to the Companions and others.