Musannaf Ibn Abi Shayba 2:81

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Muhammad ibn Talha, from Abu Sakhra Jami’ ibn Shaddad, from Musa ibn Abdullah ibn Yazid, that Sulayman ibn Surad—who had companionship [with the Prophet]—used to give the adhan in the military camp, and he would command his servant to attend to a need during his adhan.