Malik reported,

It reached him that the caller to prayer came to Umar bin Khattab to summon him for the dawn prayer and found him asleep, so he said, "Prayer is better than sleep." Umar then ordered him to include those words in the call for the dawn prayer.

وحدثني

عن مالك

أنه بلغه: أن المؤذن جاء إلى عمر بن الخطاب يؤذنه لصلاة الصبح، فوجده نائما، فقال: الصلاة خير من النوم. فأمره عمر أن يجعلها في نداء الصبح.