Musannaf Ibn Abi Shayba 13:1526

Abu Bakr narrated to us, he said: Jarir narrated to us, from Abd al-Aziz ibn Rufay, from Ata, who said: I asked him, I said: "We carry these goods for people, and we need them on the road." He said: "When you arrive, you buy for their owners what they need, and you do not withhold it." I said: "Yes." He said: "There is no harm in it; it is better for the owner of the goods."