كتاب الأذان
7
The Book of the Adhan (The Call to Prayer)
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.)'"
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 ‏.‏
GradeSahih (Darussalam)
English reference : Vol. 1, Book 7, Hadith 651
Arabic reference : Book 7, Hadith 657