Explanation
Assalatu Khairum Minan Naum means:
الصلاة خير من النوم [Assalatu Khairum Minan Naum] Prayer is better than sleep.
"assalatu khairum minan naum" (الصلوۃ خیر من النوم) is an exclusive part of call for morning prayer in Islam.
A formal call to prayer in Islam is called Azaan (اذان).
The morning prayer is called Fajr (فجر)
Assalatu Khairum Minan Naum is used only for the Fajr prayer because it was included by Umar Ibn Al-Khattab in the Azan at Fajr.
Hazart Umar (RA):
Umar was a leading companion and adviser to the Islamic prophet Muhammad, and became the second Muslim ruler after Muhammad's death and ruled for 10 years.
Converting to Islam in the 6th year after Muhammad's first revelation, he spent 18 years in companionship of Muhammad.
