Kharijah bin Zayd narrates: I saw a man who asked my father about a man who goes out on a military expedition and, on that same journey, also buys, sells and trades: what is the ruling on him? My father said to him: "We used to buy and sell with the Messenger of Allah (peace and blessings be upon him) at Tabuk, and he (peace and blessings be upon him) would see us, yet he did not forbid us."
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 4856