Is it permissible to supplicate for a destined matter to be changed for the better, such as saying: "O Lord, if You have kept him away from me because he is evil for me, then make him good by Your power and destine him to be my share?"

The basic principle for a Muslim is to ask Allah for good to be decreed and for evil to be averted. If one is unaware of the matter, then they should condition their supplication on Allah's knowledge: if it is good, they ask for it; if it is evil, they ask for it to be averted. If they do not know, they should perform Istikhara (definition) (prayer for guidance) and ask Allah to decree what is good for them wherever it may be.

It is important to differentiate between what is purely good and should be asked for without hesitation, and what has an unknown outcome, such as worldly matters whose consequences are unknown. For these, one should only ask for what contains good for them.

It is not legislated to ask Allah for something to happen in all circumstances, or to supplicate with "If it is evil, then make it good," because this was not known in the Sunnah (definition) or the words of the Salaf (pious predecessors). It contradicts the supplication of Istikhara, is considered insistence on personal desire and imitation, does not suit the servant's humility and submissiveness, and obscures the meaning of Allah's saying: (And perhaps you dislike a thing and it is good for you; and perhaps you love a thing and it is bad for you. And Allah Knows, while you know not) (2:216). It may also be considered an transgression in supplication.