The ruling on the seller saying: I sold you my house on the condition that you sell me your house

Question : It is derived that it is valid based on his statement regarding the lease, and it was said that the meaning of two sales in one sale is to say, “I sold you this for a hundred on the condition that you sell me your house for a thousand,” or on the condition that you convert it for me into gold. And whatever the case may be, it is not valid.

Answer : Yes, there is also a difference of opinion in this. If he says, “I sold you my house on the condition that you sell me your house,” the ruling is that this is not permissible.
Because it is two sales in one sale. This is closer to the first case being two sales in one sale, because you sold to him on the condition that he sells to you, so these are two sales in one sale.
But the correct view is that it is permissible, unless it is a ruse to commit riba (usury or interest). For example, if he says, “I sold you this on the condition that I lend you, say, twenty thousand, on the condition that you sell me your house.” This is not permissible because it is a loan that brings benefit. Likewise, if it includes riba, such as if he says, “I will sell you newly manufactured gold on the condition that you sell me your gold of old manufacture, and there is a difference in weight between them.” This is also not valid. Why? Because it contains riba al-fadl (usury of excess in a like-for-like exchange). So the correct view is that two sales in one sale means that conditioning one contract on another is permissible as long as it does not include something forbidden, such as riba or ambiguity. So neither of these two meanings falls under the prohibition of two sales in one sale.