Hadith: The Messenger of Allah (may Allah's peace and blessings be upon him) used to forbid us from praying or burying our deceased ones at three times: when the sun begins to rise until it is fully risen; when the sun is at its highest point in the sky at noon until it passes its zenith; and when the sun starts setting until it fully sets

عن عُقبة بن عامر الجُهَنِي رضي الله عنه قال: ثلاث ساعات كان رسول الله صلى الله عليه وسلم يَنهَانا أن نُصَلِّي فيهن، أو أن نَقْبُر فيهن مَوْتَانَا: «حِين تَطلع الشَّمس بَازِغَة حتى ترتفع، وحِين يقوم قَائم الظَّهِيرة حتى تَميل الشَّمس، وحين تَضيَّف الشمس للغُروب حتى تَغرب».
[صحيح] - [رواه مسلم]

‘Uqbah ibn ‘Āmir al-Juhani (may Allah be pleased with him) reported: The Messenger of Allah (may Allah's peace and blessings be upon him) used to forbid us from praying or burying our deceased ones at three times: when the sun begins to rise until it is fully risen; when the sun is at its highest point in the sky at noon until it passes its zenith; and when the sun starts setting until it fully sets.
[Authentic hadith] - [Narrated by Muslim]

Explanation

‘Uqbah (may Allah be pleased with him) tells us about the three hours during which the Messenger of Allah (may Allah's peace and blessings be upon him) forbade the Companions from praying or burying the dead. The meaning of "hours" here is "times", i.e. three times during which the Messenger of Allah (may Allah's peace and blessings be upon him) forbade prayer or burial of the dead, and they are strictly forbidden times. The first timing: When the sun begins to rise until it is fully risen, i.e. when the sun rises clearly in the horizon with its rays and light until it rises in the horizon. Another narration stated the measure of its rising, which is the measure of a spear. In a narration: "And it rises the measure of one or two spears," as it is in Abu Dawūd from the Hadīth of ‘Amr ibn ‘Abasah (may Allah be pleased with him). The spear is known among the Arabs, and it is a weapon which they used to use in their battles. The second timing: When the sun is at its highest point at midday, i.e. when the sun reaches its zenith. When it reaches the middle of the sky, the movement of shadow slows down until it begins to pass its zenith. So the one looking at it imagines that it has stopped, while it is actually moving but at a slow pace. So this assumed stopping is called "zenith," and during this time it is forbidden to perform voluntary prayers until the sun begins to decline, i.e. to move away from the middle of the sky, and the shadow appears from the east, and this is called the shadow of the zenith. It is a short time period, and some scholars considered it five minutes while others considered it ten minutes. The third timing: When the sun draws near to its setting until it fully sets, i.e. it begins to set and the prohibition continues until it fully sets. In these three times, two things are forbidden: 1) Supererogatory prayers, even those performed for specific reasons – such as greeting the mosque, the two Rak‘ahs performed after ablution, or the eclipse prayer – due to the generality of the Hadīth. Regarding the obligatory prayers, they are not prohibited during the forbidden times, even though the Hadīth is general, since its generality was specified in the Hadīth of Abu Qatādah (may Allah be pleased with him): "Whoever sleeps at a prayer time or forgets it should pray it once he remembers it." 2) Burial of the dead: It is not permissible to bury the dead in the prohibited times. Therefore if a corpse is brought to the graveyard during the three prohibited times, the burial should be delayed until the prohibited time passes and then it should be buried. If it happened that people began the burial before sunrise and it was prolonged for some reason, then the sun rose while they were burying, then they should continue to bury and not stop. Moreover, if they began the burying before the zenith, then they were late for some reason until the arrival of the prohibited time while they were burying, then they should continue and not stop. If they began burying after the afternoon prayer and then were delayed for some reason until they were overtaken by the prohibited time, then they should continue and not stop. That is because they did not intend to bury in these prohibited times. The same is true for the one who is praying a supererogatory prayer, and the prohibited time enters while he is praying, then he should complete his prayer. The rule is, according to scholars, completing an action started before the prohibited time is forgiven, whereas starting an action is not.