“The Prophet forbade praying after the Fajr prayer till the sun rises and after the ‘Asr prayer till the sun sets.”
Hadith no. 556 as above.
Narrated Hisham’s father:
Ibn ‘Umar said, “Allah’s Apostle said, ‘Do not pray at the time of sunrise and at the time of sunset.’ ” Ibn ‘Umar said, “Allah’s Apostle said, ‘If the edge of the sun appears (above the horizon) delay the prayer till it becomes high, and if the edge of the sun disappears, delay the prayer till it sets (disappears completely).’ “
Narrated Abu Huraira:
Allah’s Apostle forbade two kinds of sales, two kinds of dresses, and two prayers. He forbade offering prayers after the Fajr prayer till the rising of the sun and after the ‘Asr prayer till its setting. He also forbade “Ishtimal-Assama” and “al-Ihtiba” in one garment in such a way that one’s private parts are exposed towards the sky. He also forbade the sales called “Munabadha” and “Mulamasa.” (See Hadith No. 354 and 355 Vol. 3).
Reason: some people worship the sun. they specifically pray when the sun is rising/setting. Muslims are ordered to differentiate.