Musnad Ahmad 32:786

'Abd al-Samad narrated to us, Za'idah narrated to us, al-A'mash narrated to us, he said: It was narrated to me from Anas, from the Prophet, may Allah bless him and grant him peace, that he said: "The people with the longest necks on the Day of Resurrection will be the callers to prayer (mu'adhdhins)."