Is it permissible to sell a house that a man bought with the intention of reselling it, along with his first house and paying an additional sum, and how is the Zakat for this sale to be paid?

First: It is permissible to sell one house for another, with or without a cash difference, unless the second sale is conditional or colluded upon in the first contract.

Second: For someone who buys a house with the intention of selling it for profit, trade zakat (definition) becomes obligatory under certain conditions: 1. That a lunar year (hawl) passes on it, beginning from the date of purchase. 2. That it reaches the nisab (definition) (which is equivalent to 595 grams of silver). When the hawl is complete, the value of the house is assessed, and its zakat is paid at the rate of one-quarter of one-tenth (2.5%) of this value. If the house is sold before the completion of the hawl, and the buyer intended to own it (not for trade), then there is no zakat on the house itself. Zakat would be obligatory on the cash amount if it reaches the nisab and a hawl passes on it. However, if the intention was for trade, then the hawl is not interrupted. The value of the house is assessed, and the remaining cash amount is added to it, and zakat is paid on the total sum.