Salat al-Zuhr (Noon)

The Noon Contact Prayer (Salat al-Zuhr) is specified verse:

[17:78] You shall observe the Contact Prayer (Salat) when the sun declines from its highest point at noon, as it moves towards sunset. You shall also observe (the recitation of) the Quran at dawn. (Reciting) the Quran at dawn is witnessed.

أَقِمِ ٱلصَّلَوٰةَ لِدُلُوكِ ٱلشَّمْسِ إِلَىٰ غَسَقِ ٱلَّيْلِ وَقُرْءَانَ ٱلْفَجْرِ إِنَّ قُرْءَانَ ٱلْفَجْرِ كَانَ مَشْهُودًا

1	aqimi	أَقِمِ	Observe
2	l-ṣalata	ٱلصَّلَوٰةَ	the Contact Prayer (Salat),
3	lidulūki	لِدُلُوكِ	at (the) declining [from its highest point] (of)
4	l-shamsi	ٱلشَّمْسِ	the sun
5	ilā	إِلَىٰ	towards
6	ghasaqi	غَسَقِ	(the) obscuring / darkness (of)
7	al-layli	ٱلَّيْلِ	the night (sunset)

The term "lidulūki l-shamsi" ( لِدُلُوكِ ٱلشَّمْسِ ) means simply the decline of the sun. This would correspond to when the sun reaches its zenith and begins its decline.