Musannaf Ibn Abi Shayba 3:1594

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Hisham, from his father, from Zubayd ibn al-Salt, that: Umar washed what he saw on his garment, and he sprinkled water on what he did not see. And he repeated [the prayer] after the forenoon had risen, while he was settled.