I say, and with God's success: The minimum threshold for gold is twenty mithqals, and the mithqal is an ancient gold dinar, and the dinar equals (5) grams, thus the minimum threshold is (100) grams of gold, as recorded by the Mufti of Homs, the scholar, reciter, and jurist Sheikh Abdul Aziz Ayoun Al-Soud in his message "The Legal Measurements"; see: Hashiyat Al-Labab (341:2); it was narrated by Ali (may Allah be pleased with him) that he said: "If you have two hundred dirhams and a year has passed over them, then there are five dirhams due, and there is nothing due on you regarding gold until you have twenty dinars. If you have twenty dinars and a year has passed over them, then there is due half a dinar." This is found in Sunan Abu Dawood 2: 100, and the Selected Hadiths 2: 154, and Allah knows best.