Hisham bin Yusuf says that the people of Hufash brought out a document of Sayyiduna Abu Bakr (may Allah be pleased with him) on a piece of leather, in which they were ordered to pay the tithe on wars.
Imam al-Shafi'i (may Allah have mercy on him) says: I do not know whether this ruling is established or not, and it is acted upon in Yemen. If it is established, then there is zakah in it, whether its amount be little or much.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / A3