'Abdullah b. Mas'ud (Allah be pleased with him) reported that the Messenger of Allah (ﷺ) had said:Bilal would pronounce Adhan (at the fag end of the night in order to inform the people about the time of the Sahri). So you eat and drink till you hear the Adhan of Ibn Umm Maktum (which was pro- nounced at the conclusion of the Sahri and the commencement of the fast).
حَدَّثَنَا يَحْيَى بْنُ يَحْيَى، وَمُحَمَّدُ بْنُ رُمْحٍ، قَالاَ أَخْبَرَنَا اللَّيْثُ، ح وَحَدَّثَنَا قُتَيْبَةُ بْنُ، سَعِيدٍ حَدَّثَنَا لَيْثٌ، عَنِ ابْنِ شِهَابٍ، عَنْ سَالِمِ بْنِ عَبْدِ اللَّهِ، عَنْ عَبْدِ اللَّهِ، - رضى الله عنه - عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم أَنَّهُ قَالَ " إِنَّ بِلاَلاً يُؤَذِّنُ بِلَيْلٍ فَكُلُوا وَاشْرَبُوا حَتَّى تَسْمَعُوا تَأْذِينَ ابْنِ أُمِّ مَكْتُومٍ " .
Muslim
The Book of Fasting • Hadith 42