Musannaf Ibn Abi Shayba 3:3276

Yazid ibn Harun narrated to us, he said: Sharik narrated to us, he said: I said to Abu Ishaq, "How did Ali and Abdullah use to say the Takbir?" He said: "They used to say: '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.'"