Is the fast valid for someone who intended to fast the Day of Ashura in the morning after it became clear to him that it was the Day of Ashura, and he had not eaten anything? And will he achieve thereby the virtue of expiating the sins of the past year?

The intention for a supererogatory fast (nafila) can be made during the day, as long as the fasting person has not consumed any proscribed substances after dawn. However, the reward for the fast is calculated only from the time of the intention, not from the beginning of the day. Based on this, whoever intends to fast Ashura during the day will not receive the reward of expiating the sins of the past year, but will attain the general reward for fasting in the month of Muharram.