أَخْبَرَنَا سُوَيْدُ بْنُ نَصْرٍ، قَالَ أَنْبَأَنَا عَبْدُ اللَّهِ، عَنْ سُفْيَانَ، عَنْ أَبِي جَعْفَرٍ، عَنْ أَبِي سَلْمَانَ، عَنْ أَبِي مَحْذُورَةَ، قَالَ كُنْتُ أُؤَذِّنُ لِرَسُولِ اللَّهِ صلى الله عليه وسلم وَكُنْتُ أَقُولُ فِي أَذَانِ الْفَجْرِ الأَوَّلِ حَىَّ عَلَى الْفَلاَحِ الصَّلاَةُ خَيْرٌ مِنَ النَّوْمِ الصَّلاَةُ خَيْرٌ مِنَ النَّوْمِ اللَّهُ أَكْبَرُ اللَّهُ أَكْبَرُ لاَ إِلَهَ إِلاَّ اللَّهُ ‏.‏

It was narrated that Abu Mahdhurah said: "I used to call the Adhan for the Messenger of Allah (PBUH) and in the first Adhan of Fajr I used to Say: 'Hayya 'ala al-falah, as-salatu khairun minan-nawm, as-salatu khairun minan-nawm, Allahu Akbar Allahu Akbar, la ilaha illallah (Come to prosperity, prayer is better than sleep, prayer is better than sleep, Allah is the Greatest, Allah is the Greatest, there is none worthy of worship except Allah).'" Translation Not Available

Book reference: Sunan An Nisai Book 7 Hadith 654
Web reference: Sunan An Nisai Volume 1 Book 7 Hadith 648