It is obligatory for the fasting person to refrain from things which break the fast from the true dawn until the sun sets. What is means is when dawn breaks, not the adhaan “and eat and drink until the white thread (light) of dawn appears to you distinct from the black thread (darkness of night)” [al-Baqarah 2:187]
4:08, or before the beginning of the Fajr period, which is about 1.5 hours before the sunrise.
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