Muwatta Malik, Book 15, Hadith 49 (USC-MSA) ⓘ

Yahya related to me from Malik from Abdullah ibn Dinar from Abdullah ibn Umar that Umar ibn al-Khattab used to say, "Do not intend to do your prayer at either sunrise or sunset, for the horns of Shaytan rise with the rising of the sun and set with its setting." Umar used to beat people for that kind of prayer.

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ عَبْدِ اللَّهِ بْنِ دِينَارٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ، أَنَّ عُمَرَ بْنَ الْخَطَّابِ، كَانَ يَقُولُ لاَ تَحَرَّوْا بِصَلاَتِكُمْ طُلُوعَ الشَّمْسِ وَلاَ غُرُوبَهَا فَإِنَّ الشَّيْطَانَ يَطْلُعُ قَرْنَاهُ مَعَ طُلُوعِ الشَّمْسِ وَيَغْرُبَانِ مَعَ غُرُوبِهَا وَكَانَ يَضْرِبُ النَّاسَ عَلَى تِلْكَ الصَّلاَةِ ‏.‏