Sayyiduna Abu Hurayrah (may Allah be pleased with him) says: The muezzin would call the adhan when dawn broke, and the Messenger of Allah (peace and blessings be upon him) said: "When one of you hears the call while the vessel is in his hand, let him fulfil his need."
If this is authentic, the generality of the people of knowledge understand it to mean that he (peace and blessings be upon him) knew that the caller was calling before dawn broke, so that his drinking would take place just before dawn. The narrator's words "the muezzins used to call the adhan when dawn broke" may be a disconnected report from someone below Abu Hurayrah, or a report about the second adhan, while the Prophet's (peace and blessings be upon him) words "When one of you hears the call while the vessel is in his hand" refer to the first call, so that it agrees with the other reports.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8020