Sa’ad, from Yaqub ibn Yazid, from Ali ibn Jafar, from al-Hakam ibn Bahlul, from Abu Hammam, from al-Hasan ibn Ziyad, from Abu Abdillah عليه السلام, peace be upon him, who said: Imam al-Sadiq عليه السلام said: “A man came to the Commander of the Faithful عليه السلام, peace be upon him, and said: ‘O Commander of the Faithful, I have acquired wealth, and I do not know its lawful from its unlawful.’” Imam Ali عليه السلام said to him: “Take out the fifth (al-khums) from that wealth, for Allah سبحانه وتعالى, Mighty and Majestic, has been pleased with the fifth from the wealth, and avoid what its owner used to know.” – meaning wealth whose rightful owner is known, that should not simply be purified by paying khums; it should be avoided/returned/dealt with separately.