Musannaf Ibn Abi Shayba 2:3

Abu Bakr narrated to us, he said: 'Ulayyah narrated to us, from Ayyub, from Nafi', from Ibn 'Umar, he said: The Adhan of Ibn 'Umar was: "Allah is the Greatest, Allah is the Greatest, Allah is the Greatest. I bear witness that there is no god but Allah, I bear witness that there is no god but Allah, I bear witness that there is no god but Allah," (three times). "I bear witness that Muhammad is the Messenger of Allah, I bear witness that Muhammad is the Messenger of Allah, I bear witness that Muhammad is the Messenger of Allah," (three times). "Hasten to the prayer," (three times). "Hasten to success," (three times). "Allah is the Greatest." I think he said: "There is no god but Allah."