Salim narrates from his father (Abdullah bin Umar, may Allah be pleased with them both) that Sayyiduna Umar (may Allah be pleased with him) used to collect a twentieth on wheat and oil from the people of the Nabat, so that they would bring more goods to Madinah, and he used to collect a tenth on qitniyyah (pulses).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجزية / 18766