Hadith 5:455
Yazid ibn Harun narrated to us, he said: Hisham narrated to us, from Muhammad, from Ubaydah, who said: Ali was asked about a man who has a speculative debt: "Should he pay Zakat on it?" He said: "If he is truthful, then let him pay Zakat on it for what has passed when he collects it."
حدثنا يزيد بن هارون قال حدثنا هشام عن محمد عن عبيدة قال سئل علي عن الرجل يكون له الدين المظنون أيزكيه فقال إن كان صادقا فليزكه لما مضى إذا قبضه