Muwatta Imam Malik (Riwayat Yahya)

Imam Malik, may Allah have mercy on him, said: If a person has goats less than the nisab, and one day before the collector comes, those goats give birth and the nisab is completed, then zakat will be obligatory on him, because the offspring are included among the goats. And this issue is contrary to the issue where a person has goats less than the nisab, then due to purchase, inheritance, or gift, more goats come to him. A similar example is that a person has some goods whose value is less than the nisab, then he sells them with such a profit that it reaches the nisab, so zakat will be obligatory on the profit along with the principal. And if the profit comes to him as a gift or inheritance, then zakat will not be obligatory until a year passes over it or by the force of inheritance.