The Book of the Adhan (The Call to Prayer)
7/16. Chapter:
The Final Words Of The Adhan
Sunan an-Nasai
أَخْبَرَنَا سُوَيْدٌ، قَالَ أَنْبَأَنَا عَبْدُ اللَّهِ، عَنْ سُفْيَانَ، عَنْ مَنْصُورٍ، عَنْ إِبْرَاهِيمَ، عَنِ الأَسْوَدِ، قَالَ كَانَ آخِرُ أَذَانِ بِلاَلٍ اللَّهُ أَكْبَرُ اللَّهُ أَكْبَرُ لاَ إِلَهَ إِلاَّ اللَّهُ .
It was narrated that Al-Aswad said: "The final words of the Adhan of Bilal were: 'Allahu Akbar, Allahu Akbar, Allahu Akbar; La ilaha illallah (Allah is the Greatest, Allah is the Greatest, there is none worthy of worship except Allah.)'"
Reference : Sunan an-Nasa'i 650In-book reference : Book 7, Hadith 25English translation : Vol. 1, Book 7, Hadith 651