When does the time for Dhuhr prayer begin?
Chapter on Prayer Times
Al-Mughni
Book of Prayer
Primary text
The time for the Dhuhr prayer, and indeed all obligatory prayers, begins immediately upon the sun's setting (Zawal al-Shams) for those obligated to perform it. This is proven by the Divine command: {Establish the prayer at the setting of the sun} [Al-Isra: 78]. An imperative command necessitates immediate fulfillment. Furthermore, the entry of the time is the cause for the obligation, and its ruling must follow immediately upon its existence. Additionally, the intention (Niyyah) of the obligatory prayer is a prerequisite, and if it were not obligatory immediately, it would be valid without the intention required for an obligation, unlike the supererogatory prayer.
Supporting text
Abu Hanifa holds that delaying the prayer is permissible if the remaining time is insufficient for performing more than one prayer. He argues that at the beginning of the time, one has the choice to perform it or omit it, thus it is not strictly obligatory like a voluntary prayer.