Miqsam narrates from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that concerning the saying of Allah Almighty: "And give its due on the day of its harvest." [Surah al-An'am: 141], he said: It refers to the tenth ('ushr) and half the tenth (nisf al-'ushr).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7501