Hadith 5:755
Ghundar narrated to us, from Shu'bah, who said: I asked Hammad about a man who has a debt upon him, while in his hand is wealth; should he pay Zakat on it? He said: "Yes, he must pay its Zakat. Do you not see that he is a guarantor?" And I asked Rabi'ah, and he said the same as the statement of Hammad.
حدثنا غندر عن شعبة قال سألت حمادا عن الرجل يكون عليه الدين وفي يده مال أيزكيه قال نعم عليه زكاته ألا ترى أنه ضامن وسألت ربيعة فقال مثل قول حماد