Narrated Ar-Rubai binti Mu'awwidh that Rasullah (pbuh) sent a messenger to the village of the Ansar in the morning of the day of Ashura to announce, “Whoever has eaten something should not eat but complete the fast, and whoever is observing the fast should complete it.”
She further said, “Since then we used to observe fast on that day regularly and also make our children observe fast. We used to make toys of wool for the boys and if anyone of them cried for food, he was given those toys till it was the time of the iftar.”
Look how the great companions of Rasulullah (pbuh) took every act of worship seriously and taught their children even when they were very young!
According to the scholars of Islam, the fast of children is not obligatory but recommended. According to Imam Shafii, children should be ordered to fast after seven or ten years old if they are physically strong enough; according to Ishak, children should be ordered to fast from twelve years old; according to Imam Ahmad ibn Hanbal, children should be ordered to fast from ten years old. Evzai said: “If you make your children fast, three consecutive days is recommended.”
However, we should not cause children to become weak, and also we should remember that even the travelers are permitted not to fast. We should not forget that Allah says in the Qur'an: “Allah desireth for you ease; He desireth not hardship for you.”
According to the narration of Ibn Abbas: “The Prophet (pbuh) came to Al-Madina and s.a.w. the Jews fasting on the day of Ashura. He asked them about that. They replied, ‘This is a good day, the day on which Allah rescued Bani Israel from their enemy. So Moses (pbuh) observed fast on this day.’ The Prophet (pbuh) said: ‘We have more claim over Moses (pbuh) than you., So the Prophet (pbuh) observed fast on that day and ordered the Muslims to fast on that day.”
It is narrated that on this day (Muharram 10th) the repentance of Adam (pbuh) was accepted, Adam (pbuh) reached the level of prophets, Idris (pbuh) was raised to a high place, the ark of Noah (pbuh) was saved, Abraham(pbuh) was rescued from the fire, Moses (pbuh) was given the Torah, Joseph (pbuh) was saved from the prison, the sight of Jacob (pbuh) was restored, Job (pbuh) was cured, Jonah (pbuh) was saved from the belly of the fish, the Red Sea was divided in front of the Children of Israel and they were saved from the armies of Pharaoh, David (pbuh) was forgiven, Solomon (pbuh) was given his throne and wealth, the past and future sins of Muhammad (pbuh) were forgiven, the earth was created, the first rain fell on the earth.
Ibn Abbas narrated that in order to be different from the Jews we should not fast only on the 10th of Muharram, but on the 9th and 10th, or the 10th and 11th.
Ar Rawzu’l Faik tells this story in his book:
“There was a wealthy man in Basra. Every year on the day of Ashura he used to invite his Muslim brothers to his house, and read the Qur'an all night, help the needy, the poor and the widows. In his neighborhood, there was a man and his daughter, both of whom were paralyzed and could not walk. That night the girl asked her father, ‘O father, why did our neighbor gather so many people in his house and read the Qur'an all night?’ The father answered, ‘Today is the day of Ashura, which has many blessings, and this day is very important before Allah.’
Later, her father went to sleep but the daughter could not. She was listening to the Qur'an and the dhikr. When she heard the supplication of Hatim, when the recitation of the whole Qur'an was finished, she raised her hands and said, “O Allah, for the sake of this night, and for the sake of Your servants who don't sleep tonight to read the Qur'an, make me healthy again!”
When her father saw her the next morning, he was surprised and asked how she had been restored to health. She said, ‘I begged Allah through the blessings of this night, and He gave my health back.’”