What is the ruling regarding the prayer of Dhuhr (Midday Prayer)?

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The time for Dhuhr begins immediately upon the sun's zenith passage (Zawāl al-Shams). This is the consensus opinion held by scholars such as Ibn al-Mundhir and Ibn Abd al-Barr. The justification for commencing the discussion with Dhuhr is threefold: the Archangel Jibril commenced leading the Prophet (peace be upon him) in prayer with Dhuhr in the narration of Ibn Abbas; the Prophet (peace be upon him) began teaching the Companions the prayer timings with Dhuhr, as narrated by Buraydah and others; and the Companions began enumerating the times starting with Dhuhr when questioned, as seen in the narrations of Abu Burzah and Jābir. Dhuhr is also known as Al-Ula or Al-Hajirah. Evidence includes the narration from Ibn Abbas stating Jibril led him in Dhuhr when the shadow (fay') was the length of a sandal strap, and the narration from Buraydah where the Prophet (peace be upon him) instructed to perform Dhuhr after the sun had passed its zenith, stating that the prayer time is between the two instances demonstrated over two days.