Is that when the Prophet (s) entered Madinat munawwara after migration from Mecca to Madina, and on the 10th of Muharram which is tomorrow, he saw the Jews fasting, and he asked why they were fasting that day. Of course the Prophet (s) knows but he wants to teach the Sahaba. He said, “Why are they fasting on the day of the 10th of Muharram?” and they said that on that day Allah swt saved Sayyidina Musa from Fira’un, and that is why it is showing thanking Allah for his favor that is why they are fasting on that day. And the Prophet (s) said, "nahnu ahaqq `an Musa minhum, we have more rights on Sayyidina Musa than they do," and he fasted that day, the 10th of Muharram.
And he said that on that day Allah will forgive the sins of the last year, anyone who fasts that day, Allah swt will forgive him all the sins that he did in the past year. So one day is equal to the forgiveness of one year.
So it is very recommended to fast on that day.
And on the same occasion on that day Sayyidina Husayn was killed that is why also it is an important day. And on that day many important events occurred. And it coincides on the day of Friday this year, and that coincides with the same day that Sayyidina Musa was saved, the same day that Sayyidina Ibrahim was saved from Nimrud, the same day Sayyidina Nuh was saved from the flood, the same day that Sayyidina Adam was sent to the earth and the same day that Sayyidina `Isa was lifted to heaven and so that day is a very important day, and so it is highly recommended to fast on that day so that is forgiveness for one year and so tonight we are not going to do a suhbat but we do dhikr and we ask Allah to accept from all of us. If people will fast on the intention that Allah take their difficulties their problems and Allah change their fastings of Ramadan from imitational fasting to real fasting. And asking Allah to forgive them their sins from their childhood were born until their death, then Allah might… it is not might.., but Allah will accept, because Allah is merciful with His servants. May Allah forgive us all.