This hadith has been narrated on the authority of Sulaiman Taimi with the same chain of transmitters and, at the end, it was said that the first Adhan was meant to awaken those who were in slumber amongst them and in order to make them turn who stand in (prayer) among them (towards food at the commencement of the fast). Jarir (one of the narrators) said that the Messenger (ﷺ) did not say like this but he said like it (true dawn) that the streaks of (true dawn ) are horizontal and not vertical.
وَحَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا مُعْتَمِرُ بْنُ سُلَيْمَانَ، ح وَحَدَّثَنَا إِسْحَاقُ بْنُ، إِبْرَاهِيمَ أَخْبَرَنَا جَرِيرٌ، وَالْمُعْتَمِرُ بْنُ سُلَيْمَانَ، كِلاَهُمَا عَنْ سُلَيْمَانَ التَّيْمِيِّ، بِهَذَا الإِسْنَادِ . وَانْتَهَى حَدِيثُ الْمُعْتَمِرِ عِنْدَ قَوْلِهِ " يُنَبِّهُ نَائِمَكُمْ وَيَرْجِعُ قَائِمَكُمْ " . وَقَالَ إِسْحَاقُ قَالَ جَرِيرٌ فِي حَدِيثِهِ " وَلَيْسَ أَنْ يَقُولَ هَكَذَا وَلَكِنْ يَقُولُ هَكَذَا " . يَعْنِي الْفَجْرَ هُوَ الْمُعْتَرِضُ وَلَيْسَ بِالْمُسْتَطِيلِ .
Muslim
The Book of Fasting • Hadith 49