Is zakat obligatory upon a man who sold sheep that reached the nisab, on credit for one year?

If a man sells his sheep after a year has passed and before paying their zakat (definition), the zakat on the price becomes obligatory for him at the time of sale. However, if the payment is deferred, he is not obligated to pay its zakat until he receives it, as chosen by Imam Malik. It is stated in Al-Mudawwanah that he pays a single zakat upon receiving it, which is the zakat that became due on him when he sold the sheep.