Musannaf Ibn Abi Shayba 3:5561

Hafs narrated to us, from Hisham ibn Urwah, from his father, from Abdullah ibn al-Arqam, who said: He went out for Umrah with his companions, and he gave the Adhan and the Iqamah. Then he said to some of his companions: "Step forward, for I heard the Messenger of Allah (peace and blessings of Allah be upon him) say: 'When the prayer is present and one of you desires to relieve himself, then begin with relieving yourself.'"