قَالَ مَوْعِدُكُمْ يَوْمُ الزِّينَةِ
(Musa) said;"Your appointed meeting is the day of the festival,
That was the day of their celebration and their New Year's festivity. It was a holiday for them when they took vacation from their work and came together for a large gathering.
This day was selected so that all of the people could witness the power of Allah to do whatever He wills. They would see the miracles of the prophets and the futility of magic to contest the supernatural prophetic powers.
This is why Musa said,
وَأَن يُحْشَرَ النَّاسُ
and let the people assemble,
meaning all of them.
ضُحًى
when the sun has risen (forenoon).
meaning in the morning, just before noon.
In this way the contest will be most visible, well lit, apparent and obvious in plain view. This is the way of the Prophets. Their work is always clear and apparent. It is never something hidden, or something for sale. This is why he did not say that the meeting should be at night, but rather, it was to be held during the bright part of the day.
Ibn Abbas said,
"The day of their festivity was the day of `Ashura'."
As-Suddi, Qatadah and Ibn Zayd said,
"It was the day of their great celebration."
Sa`id bin Jubayr said,
"It was the day of their great bazaar."
These statements are not contradictory.
I say that Allah destroyed Fir`awn and his armies on a day similar to this, just as is confirmed in the Sahih.
Abdur-Rahman bin Zayd bin Aslam said,
"It was a flat place where all of the people were on the same level, having an equal view of the event. There was nothing there that would obstruct the view so that some people could see what others did not.