الْيَوْمَ the day in Arabic

فَلَمَّا أَمْسَى النَّاسُ الْيَوْمَ الَّذِي فُتِحَتْ عَلَيْهِمْ أَوْقَدُوا نِيرَانًا كَثِيرَةً

When evening fell on the day that had been opened to them, the people kindled many fires.

الْيَوْمَ the day

The al- prefix makes this definite, the particular day, and its -a ending casts it into the time-adverb role, telling WHEN, on the day that. Arabic marks a 'when' noun with this accusative shape rather than a preposition.

From The Martyr's Reward

ثُمَّ قَالَ لَهُ إِذَا جَلَسْتَ الْيَوْمَ فِي الْمَجْلِسِ

Then he said to him, 'If you sit in the council today.'

الْيَوْمَ today

A time-noun, 'today', pressed into adverb duty and so wearing the object-style ending Arabic uses to turn a noun into a 'when'. It pins the sitting to a particular day without any separate word for 'on'.

From Sheba's Garden and Destruction

فيقول إن ربي غضب اليوم غضباً لم يغضب قبله مثله، ولن يغضب بعده مثله، وإنه قد كانت لي دعوة دعوت بها على قومي،

He says, "My Lord was angry today with an anger like none before it, and none like it will be after it, and indeed there was for me a supplication which I invoked against my people,"

الْيَوْمَ today

A time noun made definite by al- 'the', set in the accusative to work as a 'when' adverb: 'today'. The accusative is what lets a noun pin down the time of the action without a preposition.

From The Prophet's Intercession

فيقول عيسى إن ربي غضب اليوم غضباً لم يغضب قبله مثله، ولن يغضب بعده مثله ولم يذكر ذنباً،

Then Jesus will say, "My Lord was angry today with an anger like none before it, and none like it will be after it, and he did not mention any sin."

الْيَوْمَ today

A time-word in the adverb form pinning the anger to 'today'; the special ending flags it as a when. It anchors the verb to the present day.

From The Prophet's Intercession