مِشْكَاةُ الْمَصَابِيحِ
Mishkat al-Masabih 652
Prayer
The Call to Prayer - Section 3
وَعَن مَالك بَلَغَهُ أَنَّ الْمُؤَذِّنَ جَاءَ عُمَرَ يُؤْذِنُهُ لِصَلَاةِ الصُّبْحِ فَوَجَدَهُ نَائِمًا فَقَالَ: الصَّلَاةُ خَيْرٌ مِنَ النَّوْمِ فَأَمَرَهُ عُمَرُ أَنْ يَجْعَلَهَا فِي نِدَاءِ الصُّبْح. رَوَاهُ فِي الْمُوَطَّأ
Malik heard that the mu'adhdhin came to ‘Umar to call him to the Morning Prayer. Finding him asleep, he said, “Prayer is better than sleep," and ‘Umar commanded him to include it in the call to Morning Prayer. He transmitted it in al-Muwatta’.
Mishkat al-Masabih, 652ضَعِيف (الألباني)