Musannaf Ibn Abi Shayba 36:332

'Abd al-Rahim ibn Sulayman narrated to us, from 'Ubayd Allah, from Nafi', from Ibn 'Umar, who said: The Messenger of Allah (may Allah bless him and grant him peace) sent us in a military expedition to Najd. Our shares reached twelve camels, and the Messenger of Allah (may Allah bless him and grant him peace) gave us an extra camel each as a reward (nafal).