It is narrated from Sayyiduna Anas (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Indeed, Bilal gives the call to prayer (adhan) while it is still night (that is, before true dawn), so keep eating and drinking until Ibn Umm Maktum gives the call to prayer."
Al-Bazzar recorded it, and its narrators are the narrators of the Sahih.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصيام / 4860