Umar commanded the mu'adhdhin add “Prayer is better than sleep," to the Subh call to prayer
Muwatta Malik Book 3, Hadith 8
Malik ibn Anas 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.

وَحَدَّثَنِي عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ الْمُؤَذِّنَ، جَاءَ إِلَى عُمَرَ بْنِ الْخَطَّابِ يُؤْذِنُهُ لِصَلاَةِ الصُّبْحِ فَوَجَدَهُ نَائِمًا فَقَالَ الصَّلاَةُ خَيْرٌ مِنَ النَّوْمِ ‏.‏ فَأَمَرَهُ عُمَرُ أَنْ يَجْعَلَهَا فِي نِدَاءِ الصُّبْحِ ‏.‏
Reference  : Muwatta Malik Book 3, Hadith 8
In-book reference  : Book 3, Hadith 154
Note: Everything to the contrary appears to only be reported by one narrator: Abu Mahdhurah.
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