[20].Surah Taha [Tâ-Hâ]: Ayat 77-78

Ayat 77. And indeed We inspired Mûsa (Moses) (saying): "Travel by night with Ibadi (My slaves) and strike a dry path for them in the sea, fearing neither to be overtaken [by Firaun (Pharaoh)] nor being afraid (of drowning in the sea)."

Ayat 78. Then Firaun (Pharaoh) pursued them with his hosts, but the sea-water completely overwhelmed them and covered them up. 

[Tafseer] Time passes and at last Moses is commanded to leave Egypt with his people by night. They were cross the Red Sea into the Sinai Peninsula . They were told to have no fear of Pharaoh or of the sea or of t he unknown desert country of Sinai into which they were going. They crossed dry-shod, while Pharaoh, who came in pursuit with his troops, was overwhelmed by the sea. He and his men all perished. There is no emphasis on this episode here. But the emphasis is laid on the hard task which Moses had with his own people after he had delivered them from the Egyptian bondage. Then Pharaoh pursued them with his forces, but the waters completely overwhelmed them and covered them up.

Hazrat Ibn Abbas (May Allah be pleased with him) reported: The Messenger of Allah [SAWW](PBUH) observed Saum (fasting) on the day of `Ashura' and commanded us to fast on this day.  [Al-Bukhari Hadith # 2004] 

Lesson : as mentioned above in Surah Taha Ayat 78."Then Firaun (Pharaoh) pursued them with his hosts, but the sea-water completely overwhelmed them and covered them up" Ashura' 10th of Muharram. In another Hadith, it is stated that when the Prophet (PBUH) emigrated from Makkah to Al-Madinah, he saw that the Jews were fasting on this day. He asked them why they did this on that day, and they told him that they did it for the reason that Allah granted Prophet Musa emancipation from Pharaoh on this day, and so they observed Saum in token of their joy. On this, he (PBUH) said that in this happiness of Prophet Musa, Muslims have a greater right to observe Saum than the Jews. Consequently, he also observed Saum on 10th of Muharram. Then, he said that if he lived the following year, he would observe Saum on 9th of Muharram also so that they would make themselves different from the Jews. According to another Hadith, he (PBUH) ordained the Muslims to observe Saum on `Ashura' and in addition one more Saum on 9th or 11th of Muharram in opposition to the Jews.