Musannaf Ibn Abi Shayba 28:664

Waki’ narrated to us, he said: Al-Sabah ibn Thabit al-Bajali narrated to us, he said: I heard al-Sha’bi saying: Al-Mundhir ibn Abi Humsa went out in pursuit of the enemy, and the noble horses caught up, while the pack horses lagged behind. So he assigned a share [of the spoils] to the noble horses and did not assign a share to the pack horses. He wrote to Umar regarding that, and that pleased Umar. Umar said in the narration of one of them: "May the mother of the Wadi’i be bereaved of him; he has indeed attained [a correct judgment] through it."