Is the husband's action of giving his first wife a new car without the knowledge of his second wife, who drives the old car, considered an unjust and unfair act that necessitates equitable treatment between them?

The justice obligatory upon the husband is justice in expenditure, lodging, housing, and clothing. As for your objection to what your husband gave to his first wife, namely a car and money, under the pretext that it was an injustice, it is not well-founded for two reasons:

1. Justice or equality is not obligatory in gifts between wives, even though justice in them is commendable and an ethical virtue. Scholars have deduced this from the Prophet's preference for some of his wives in the wedding feast, and they permitted singling out some wives for gifts and presents. 2. What your husband gave to his first wife was before he consummated the marriage with you. Justice in obligatory matters is not required between a woman with whom a marriage contract has been concluded and one with whom it has been consummated. The obligation of justice in gifts is waived if the gift was given before consummating the marriage with the other wife, especially in what is known as "al-ridhwa" (a gift given to appease) to appease the first wife.