The Adhan of Bilal may not mislead you with regard to your food at the commencement of the fast, nor the vertical (streaks) of whiteness in the horizon (for it is an indication of false dawn). You should stop eating (food) till (the whiteness) spreads like it. Hammad narrated it and with the gesture of his band he explained, the horizontal position (of the streaks of light).  

قَالَ رَسُولُ اللَّهِ ﷺ لاَ يَغُرَّنَّكُمْ مِنْ سَحُورِكُمْ أَذَانُ بِلاَلٍ وَلاَ بَيَاضُ الأُفُقِ الْمُسْتَطِيلُ هَكَذَا حَتَّى يَسْتَطِيرَ هَكَذَا وَحَكَاهُ حَمَّادٌ بِيَدَيْهِ قَالَ يَعْنِي مُعْتَرِضًا  

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.  

قَالَ رَسُولُ اللَّهِ ﷺ لاَ يَمْنَعَنَّ مِنْ سَحُورِكُمْ أَذَانُ بِلاَلٍ وَلاَ بَيَاضُ الأُفُقِ الَّذِي هَكَذَا حَتَّى يَسْتَطِيرَ