Musannaf Ibn Abi Shaybah 10537 — Zakah on debts

It is narrated from Nafi' that Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said: The zakah of your wealth is from one full year to the next. So whatever debt is such that its recovery is certain, zakah should be paid on it as well; and for a debt about which there is doubt, he should not pay zakah on it until the debtor repays it.