Is it permissible for a high-ranking official to hire and fire according to his own desire, even if the employee works with integrity and diligence, while preferring to employ his relatives, and what are the consequences of that in this world and the hereafter?

Favoring relatives and friends over others is a clear injustice and an abuse of power. Allah has clarified the consequence of injustice, saying: (And never think that Allah is unaware of what the wrongdoers do. He only delays them for a Day when eyes will stare [in horror]), and He said: (Indeed, the wrongdoers will have a painful punishment). The Prophet, peace be upon him, said: "Beware of injustice, for injustice will be darknesses on the Day of Resurrection." Employing the unqualified and dismissing the qualified is bearing false witness. Allah has commanded justice, saying: (And when you speak, then be just, even if it is [concerning] a relative). The Prophet, peace be upon him, said: "Beware, false speech and false witness!" The official must open his doors to employees and benefit from their expertise. The Prophet, peace be upon him, said: "Whoever Allah, the Mighty and Sublime, appoints over any affair of the Muslims, and he secludes himself from their needs, their destitution, and their poverty, Allah will seclude Himself from his needs, his destitution, and his poverty."