Musannaf Ibn Abi Shayba 2:18

Abu Bakr narrated to us, he said: Abu Usamah narrated to us, from Abd al-Rahman ibn Yazid, from Makhul, who said: I stayed with him in Dabiq, and he would not add anything to the iqamah, and he would not call the adhan, and he would make it (the iqamah) single.