Ibn Majah: Hadith 707

The Prophet consulted the people as to how he could call them to the prayer. They suggested a horn, but he disliked that because of the Jews (because the Jews used a horn). Then they suggested a bell but he disliked that because of the Christians (because the Christians used a bell). Then that night the call to the prayer was shown in a dream to a man among the Ansar whose name was 'Abdullah bin Zaid, and to 'Umar bin Khattab. The Ansari man came to the Messenger of Allah at night, and the Messenger of Allah commanded Bilal to give the call to the prayer.

(Da'if)Zuhri said: "Bilal added the phrase "As-salatu khairum minan-nawm (the prayer is better than sleep)" to the call for the morning prayer, and the Messenger of Allah approved of that." 'Umar said: "O Messenger of Allah, I saw the same as he did, but he beat me to it."