Why did the Prophet (peace be upon him) command the fasting of the Day of Ashura in gratitude to Allah for saving Musa, yet he did not command the fasting of other days that witnessed the salvation of prophets such as Nuh, Ibrahim, and Isa (peace be upon them)?

That the Day of Ashura is the day Allah saved Musa from Pharaoh is established by authentic Sunnah. However, the assertion that other events, such as Noah's ark coming to rest, Noah disembarking from it, Ibrahim being saved from the fire, and Isa being raised to heaven, also occurred on the Day of Ashura, is not supported by an authentic chain of transmission, even though some narrations to this effect exist, they are weak or fabricated.

It was narrated from the Prophet, peace and blessings be upon him, that the Jews fasted the Day of Ashura because it was the day Allah saved Musa and the Children of Israel from drowning, and on which Noah's Ark came to rest on Al-Judi. So, Noah and Musa fasted it in gratitude to Allah. The Prophet, peace and blessings be upon him, then said: "I am more deserving of Musa, and more deserving of fasting this day."

Some scholars have pointed to the desirability of fasting on days when Allah's blessings are renewed for His servants. They cite as evidence the Prophet's fasting on Mondays in gratitude to Allah for his birth on that day and for the revelation of prophethood to him, as well as the fasting of Ashura in gratitude to Allah for saving Noah and Musa and their people.