Abu 'Uthman al-Nahdi عبد الرحمن بن مل - أبو عثمان النهدي · Fasting (Kitab Al-Siyam)

The adhan (call to prayer) of Bilal should not prevent you from taking a meal shortly before dawn, not does the whiteness of horizon (before dawn) in this way (vertically) until it spreads out horizontally.