Is the phrase "May God not have mercy on him," said about a person who murdered a child and his father, considered forbidden or impermissible, especially given the noble verse: "But whoever kills a believer intentionally - his recompense is Hell, wherein he will abide eternally, and Allah has become angry with him and has cursed him and has prepared for him a great punishment"?

Killing a Muslim is one of the gravest major sins. The deceased upon whom retribution (qisas) was carried out has gone on to meet what he put forth, and he was punished with the prescribed penalty (hadd) that expiates his sin, according to the more preponderant opinion. We hope for him mercy. It is incumbent to busy oneself with disseminating the texts of revelation that urge repentance and prohibit harming people and transgressing against them, for these are the most powerful in affecting souls.