Musnad Ahmad 1018:57

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from Abu Ja'far al-Madini, who said: I heard 'Umarah ibn 'Uthman ibn Hunayf, and al-Qaysi narrated to me, that he was with the Messenger of Allah (may Allah bless him and grant him peace) on a journey. He urinated, then water was brought to him. He poured it from the vessel onto his hand and washed it once, and onto his face once, and his forearms once, and he washed his feet once with both of his hands. And he said in his hadith: "He rubbed his thumb."