On the authority of Abu Hurayrah, that the Messenger of Allah, peace and blessings be upon him, said: "When the heat is intense, delay the prayer until it cools down" — Ibn Mawhab said: "the prayer" — "for the intensity of heat is from the blast of Hellfire." (1)

403 — Musa ibn Isma'il narrated to us, Hammad narrated to us, from Simak ibn Harb, from Jabir ibn Samurah: that Bilal used to give the call to prayer for Zuhr when the sun had declined from its zenith. (2)

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(1) Its chain of transmission is authentic. Al-Layth: he is Ibn Sa'd, and Ibn Shihab: he is al-Zuhri.
It was also recorded by al-Bukhari (536), Muslim (615) (180) and (181), al-Tirmidhi (157), al-Nasa'i in "al-Kubra" (1501), and Ibn Majah (678) via multiple routes from al-Zuhri, with this chain of transmission. The narration of al-Bukhari is from Sa'id alone.
It was also recorded by al-Bukhari (534), Muslim (615) (181), (182) and (183), and Ibn Majah (677) via multiple routes from Abu Hurayrah.
It is found in "Musnad Ahmad" (7130) and (7246), and "Sahih Ibn Hibban" (1507).

(2) Authentic due to corroborating evidence, and this chain of transmission is good on account of Simak ibn Harb. Hammad: he is Ibn Salamah.
It was also recorded by Muslim (606) via the route of Zuhayr ibn Mu'awiyah, from Simak, with this chain of transmission, with the addition: "and he would not give the iqamah until the Prophet, peace and blessings be upon him, came out. When he came out, he would establish the prayer upon seeing him."
It was also recorded by Muslim (618) and Ibn Majah (673) via the route of Shu'bah, from Simak, from Jabir ibn Samurah, who said: "The Prophet, peace and blessings be upon him, used to pray Zuhr when the sun had declined from its zenith."
It is found in "Musnad Ahmad" (21016).
It will come with the wording of Shu'bah under number (806) with the author.
It has a supporting witness from the hadith of Abu Barzah, which preceded under number (398).
His statement: "when the sun had declined from its zenith" — Ibn al-Athir said in "al-Nihayah": meaning: it had moved from the middle of the sky toward the west, as if it had slipped, i.e., slid. The implication of this is that he, peace and blessings be upon him, used to pray Zuhr at the beginning of its time, and this does not contradict the command to delay during intense heat, because it is possible that this was during a time of cold, or before the command to delay was given, or when the conditions for delaying were absent, since it is specific to intense heat, or to indicate permissibility.