Sunan Ibn Majah 716
سنن ابن ماجه#716Da'ifIt 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
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih
Muhammad Fouad Abd al-BaqiSahih
Zubair Ali ZaiDaif
In-book reference: 3:11