What is the criterion and standard for determining whether acquired wealth is an origin for initial wealth, such such as adding stock profits to original fabric trade profits?

Zakat is not obligatory on wealth until it reaches the minimum threshold (nisab) and a full lunar year (hawl) passes over it. If a Muslim possesses the nisab and then acquires additional wealth, if this wealth is a result of the first nisab, such as trade profits, then their hawl is one. However, if it is of a different kind, then each wealth has its own separate hawl. It is permissible for him to combine the new wealth with his old wealth to pay zakat on both together in one hawl, and this is better for the poor and easier for the owner of the wealth.