It was narrated that Muharib bin Dithar said:
"Al-Aswad bin Yazid narrated to me from Abu Mahdhurah that the final words of the Adhan are: 'La ilaha illahha (there is none worthy of worship except Allah).'"
English reference: Vol. 1, Book 7, Hadith 653
Arabic reference: Book 7, Hadith 659