´It was narrated that Bilal came to the Prophet to call him for the Fajr prayer, and was told:` "He is sleeping." He said: "As-salatu khairum minan-nawm, As-salatu khairum minan-nawm (The prayer is better than sleep, the prayer is better than sleep). These words were approved of in the Adhan for the Fajr, and that is how it remained.
Explanation & Benefits
Maulana Ataullah Sajid
Benefit:
The aforementioned narration is, according to our esteemed researcher, weak in its chain of transmission. However, Shaykh al-Albani rahimahullah has declared it authentic. See: (Takhrij Fiqh as-Sirah: 203).
Also, refer to the benefit of the previous hadith regarding (as-salatu khayrun min an-nawm).
Source: Commentary on Sunan Ibn Mājah by Mawlānā ‘Atā’ullāh Sājid, Page: 716