Shu'bi (may Allah have mercy on him) says: "The Prophet (peace be upon him) declared taking something without permission as 'nahb' (plunder), and this is not a good practice." Hakam (may Allah have mercy on him) says: Ibrahim (may Allah have mercy on him) considered it disliked.
Hadith Referenceسنن سعید بن منصور / كتاب الجهاد / 3817