And he entered the city at a time of inattention by its people and found therein two men fighting: one from his faction and one from among his enemy. And the one from his faction called for help to him against the one from his enemy, so Moses struck him and [unintentionally] killed him. [Moses] said, "This is from the work of Satan. Indeed, he is a manifest, misleading enemy."
Having described Musa's beginnings, Allah then tells us that when he reached maturity, and was complete in stature, Allah gave him Hukm and religious knowledge. Mujahid said that this means prophethood.
وَكَذَلِكَ نَجْزِى الْمُحْسِنِينَ
(And thus do We reward the doers of good.) Then Allah describes how Musa reached the status that was decreed for him, that of Prophethood and speaking to Allah, as a direct consequence of killing the Coptic, which was the reason why he left Egypt and went to Madyan. Allah says:
(And he entered the city when its people were unaware.) Ibn Jurayj narrated from `Ata' Al-Khurasani, from Ibn `Abbas, "That was between Maghrib and `Isha'." Ibn Al-Munkadir narrated from `Ata' bin Yasar from Ibn `Abbas, "That was in the middle of the day." This was also the view of Sa`id bin Jubayr, `Ikrimah, As-Suddi and Qatadah.
وَلَمَّا بَلَغَ أَشُدَّهُ وَاسْتَوَىٰ (And when he reached his maturity and became perfect - 28:14). The literal meaning of 'ashudd (أَشُدَّ ) is to attain the peak of strength or intensity. For instance a person gradually develops from the position of juvenile weakness to the strength of adulthood. A time comes when he has attained full strength and vigour that he could achieve. That point in life is called أَشُدَّ 'ashudd. In different parts of the world and for different people this point in life varies according to climate, character of the land, race etc. Some people attain it early while others take time. ` Abd Ibn Humaid has reported that Sayyidna Ibn ` Abbas and Mujahid have placed the age of 'ashudd as 33rd year of one's life. This is called the age of perfection or the age of discernment, when the development of body stops after reaching its peak. After this age a period of hold commences, which lasts until the age of forty. This period is mentioned in the verse as اسْتَوَىٰ Istawa (translated above as became perfect). After the age of forty years the decline and weakness sets in. Hence, it can be said that 'ashudd (أَشُدَّ ) of a person starts from the age of 33 years and lasts through 40 years. (Ruh, Qurtubi).
The process of the protection of Moses is attributed entirely to God, though the sequence of events seems to have taken place as per the ‘cause and effect’ principle. One can gather from this, that in the present world of trial, God’s will manifests itself in terms of the ‘cause and effect’ chain and not in the form of supernatural wonders or magical feats. Moses was set afloat in the river in a state of helplessness, but he reached the bank safe and sound. The king ruling at the time planned to kill him, but God ordained that he be brought up by that very king. He was born in an ordinary family, but God so arranged matters that he became connected with the royal palace and became acquainted with the learning and etiquette of the highest standard. This is an example which shows that Almighty God’s powers are unlimited and there is nobody who can prevent His plans from coming into effect.
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.
