The prophet (peace and blessings be upon him) said: «Never a believer is stricken with a discomfort, an illness, an anxiety, a grief or mental worry or even the pricking of a thorn but God will expiate his sins on account of his patience» [Al-Bukhari].
«O my Lord, forgive me and turn towards me (to accept my repentance). Verily You are The Oft-Returning, the Oft-Forgiving» [At-Tirmidhi].
Ibn Al-haaj (may Allah have mercy on him) mentioned that one of the bid?ahs on ?Aashooraa? was deliberately paying zakat on this day, late or early, or slaughtering a chicken just for this occasion, or -in the case of women- using henna. (Al-madkhal)