Is the day of Ashura, which we fast, not the correct day, and that it is the tenth day of the month of Tishrei according to the Hebrew calendar, which the Umayyad caliphs changed to the tenth day of the month of Muharram?

Fasting on Ashura is a confirmed Sunnah (definition). The Prophet, peace and blessings be upon him, used to fast it before his migration. Then, after the migration, he made its fasting obligatory to reconcile with the Jews. Afterward, it became recommended after the فرض (imposition) of fasting Ramadan (definition). The claim that the Umayyads placed it in Muharram is a false assertion, as it was well-known to Quraysh and the Jews. Fasting on Ashura expiates the sins of a year. It has also been reported in Shia books that fasting on the day of Ashura expiates the sins of a year.