It is narrated from Sa’ib bin Yazid (may Allah be pleased with him) that Uthman bin Affan (may Allah be pleased with him) used to say: "This is the month of your zakat; whoever has a debt should pay it off so that only your pure wealth remains, then pay zakat from that."
Hadith Referenceمسند الإمام الشافعي / كتاب الزكاة / 692
Hadith Takhrijاسناده صحيح : اخرجه البيهقي : 4 / 148 ۔ وفى المعرفة السنن والآثار له (2369)- وعبدالرزاق (7086) ۔ و ابن ابي شيبة (1055)۔