Musannaf Ibn Abi Shayba 2:64

Abu Bakr narrated to us, he said: Ibn Numayr narrated to us, from Hallam ibn Salih, from Fa'id ibn Bukayr, he said: I went out with Hudhayfah to the mosque for the dawn prayer, and Ibn al-Tayyah, the mu'adhdhin of al-Walid ibn 'Uqbah, was calling the adhan. He was saying, "Allah is the Greatest, Allah is the Greatest, I bear witness that there is no god but Allah," while swaying with his adhan to the right and to the left. So Hudhayfah said: "Whoever Allah intends to place his provision in his voice, he does this."