Is it permissible for a father to gift his married son his private car without incurring sin upon himself or his other children?

Scholars have differed regarding the obligation of equality between children in giving gifts. The Hanafis, Malikis, and Shafi'is hold the view that equality is recommended, not obligatory, citing as evidence the preference shown by Abu Bakr and Umar to some of their children in giving gifts, and the Prophet's (peace be upon him) statement in the hadith of Nu'man ibn Bashir: "Then call someone else to bear witness to this." The preponderant opinion, however, is the obligation of equality between them, based on the Prophet's (peace be upon him) saying: "Fear Allah and be just among your children," and "Do not make me a witness to injustice." An exception to this obligation is the existence of a justifiable reason for preference, such as illness or a large family. Accordingly, there is no harm in a father gifting his son what would alleviate a need, bearing in mind that need is to be estimated proportionally.