Urwah (may Allah have mercy on him) narrates: We were with Sayyiduna Abdullah bin al-Arqam (may Allah be pleased with him) on a journey, and he used to lead the people in prayer. When the time of prayer came, he said to us: "Let one of you lead the prayer, for I heard the Messenger of Allah (peace and blessings be upon him) say: 'When the time of prayer has come and one of you needs (to relieve himself), let him first attend to his need.'"
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14049