عَنِ ابْنِ عُمَرَ عَنْ حَفْصَةَ رَضِيَ اللَّهُ عَنْهُمَا أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ كَانَ إِذَا أَذَّنَ الْمُؤَذِّنُ، صَلَّى رَكْعَتَيْنِ وَحَرَّمَ الطَّعَامَ، وَكَانَ لَا يُؤَذَّنُ حَتَّى يَطْلُعَ الْفَجْرُ
Sayyiduna Abdullah bin Umar (may Allah be pleased with him) narrates from Sayyida Hafsa (may Allah be pleased with her) that when the muezzin would call the adhan, the Prophet (peace and blessings be upon him) would perform two rak‘ahs and make food forbidden (for the fasting person), and the adhan would not be given until true dawn had appeared.