Musnad Abu Ya'la al-Mawsili 2:116

'Abd al-Ghaffar ibn 'Abd Allah al-Mawsili narrated to us, 'Ali ibn Mushir narrated to us, from 'Ubayd Allah ibn 'Umar, from Nafi', from Ibn 'Umar—perhaps from 'Umar—that he gave a horse to be ridden in the way of Allah. We used to, when we gave something to be ridden in the way of Allah, bring it to the Messenger of Allah (peace be upon him), and we would hand it over to him, and he would place it where Allah showed him. I came with the horse and handed it over to him, and he gave it to a man among his companions to ride. I encountered him selling it in the market, and I wanted to buy it. So I came to the Messenger of Allah (peace be upon him) and mentioned that to him. He said: "Do not buy it, and do not return to any part of your charity."