From Sahih Bukhari (Hadith 583):
Narrated Hisham's father:Ibn `Umar said, "Allah's Messenger (ﷺ) said, 'Do not pray at the time of sunrise and at the time of sunset.' " Ibn `Umar said, "Allah's Messenger (ﷺ) 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)
Reference: Bukhari 583