Mis'ar (may Allah have mercy on him) narrates from al-Hakam (may Allah have mercy on him) that Ibrahim (may Allah have mercy on him) said: He pays the zakah of his wealth even if he owes a debt equal to it. He said: I spoke to him about it, and he retracted it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7617