The Prophet (may Allah's peace and blessings be upon him) forbade praying after the Fajr prayer up until the sun rises, and after the ‘Asr prayer until the sun sets

In these two Hadīths, the Prophet (may Allah's peace and blessings be upon him) forbade praying after the Fajr prayer up until the sun rises and goes beyond its zenith, as seen by the normal eye for as much as the height of a spear fixed in the horizon. This period is estimated to be between 5 to 15 minutes.
He also forbade praying after the ‘Asr prayer up until the sun sets, i.e. few minutes before the Adhān of the Magrib prayer. That is because offering prayer at these two times involves resemblance to the polytheists who worship the sun upon its rising and setting, and Muslims are forbidden from acting like them in their worship, because whoever imitates a people becomes one of them.