Abu Dawud Book 2, Hadith Number 532.

Narated By Abdullah ibn Umar : Bilal made a call to prayer before the break of dawn; the Prophet (PBUH), therefore, commanded him to return and make a call: Lo! the servant of Allah (i.e. I) had slept (hence this mistake).

The version of Musa has the addition: He returned and made a call: Lo! the servant of Allah had slept.