Maliks Muwatta Book 17, Hadith Number 19.
Yahya related to me from Malik from Yazid ibn Khusayfa that he had asked Sulayman ibn Yasar whether zakat was due from a man who had wealth in hand but also owed a debt for the same amount, and he replied, “No.”
Malik said, “The position that we are agreed upon concerning a debt is that the lender of it does not pay zakat on it until he gets it back. Even if it stays with the borrower for a number of years before the lender collects it, the lender only has to pay zakat on it once. If he collects an amount of the debt which is not zakatable, and has other wealth which is zakatable, then what he has collected of the debt is added to the rest of his wealth and he pays zakat on the total sum.”
Malik continued, “If he has no ready money other than that which he has collected from his debt, and that does not reach a zakatable amount, then he does not have to pay any zakat. He must, however, keep a record of the amount that he has collected and if, later, he collects another amount which, when added to what he has already collected, brings zakat into effect, then he has to pay zakat on it.”
Malik continued, “Zakat is due on this first amount, together with what he has further collected of the debt owed to him, regardless of whether or not he has used up what he first collected. If what he takes back reaches twenty dinars of gold, or two hundred dirhams of silver he pays zakat on it. He pays zakat on anything else he takes back after that, whether it be a large or small amount, according to the amount.”
Malik said, “What shows that zakat is only taken once from a debt which is out of hand for some years before it is recovered is that if goods remain with a man for trading purposes for some years before he sells them, he only has to pay zakat on their prices once. This is because the one who is owed the debt, or owns the goods, should not have to take the zakat on the debt, or the goods, from anything else, since the zakat on anything is only taken from the thing itself, and not from anything else.”
Malik said, “Our position regarding some one who owes a debt, and has goods which are worth enough to pay off the debt, and also has an amount of ready money which is zakatable, is that he pays the zakat on the ready money which he has to hand. If, however, he only has enough goods and ready money to pay off the debt, then he does not have to pay any zakat. But if the ready money that he has reaches a zakatable amount over and above the amount of the debt that he owes, then he must pay zakat on it.”