Musannaf Ibn Abi Shayba 28:822

'Abdah ibn Sulayman narrated to us, from al-Ifriqi, from Khalid ibn Abi 'Imran, who said: I asked al-Qasim and Salim about a man who finds food in the land of the enemy, so he consumes from it and earns dirhams from it. They both said: He should put it into food that he eats, and he should not earn from it a hoard of wealth.