Musannaf Ibn Abi Shayba 28:558

'Abd al-Rahim ibn Sulayman narrated to us, from Hajjaj, from Nafi', from Ibn 'Umar, who said: Ibn 'Umar went on a military expedition to Iraq. 'Umar said to him, "It has reached me that you engaged in single combat with a Dihqan." He said, "Yes." That pleased him, so he granted him his spoils as a reward.