Musannaf Ibn Abi Shayba 3:3256

Abu al-Ahwas narrated to us, from Abu Ishaq, from al-Aswad, who said: Abdullah used to say the takbir from the Fajr prayer on the day of Arafah until the Asr prayer of the day of Sacrifice (al-Nahr). He would say: Allah is the Greatest, Allah is the Greatest, Allah is the Greatest. There is no god but Allah, and Allah is the Greatest, Allah is the Greatest, and to Allah belongs all praise.