What is the authenticity of the hadith: "Five things for which there is no expiation: polytheism with Allah, slandering a believer..." and what is the meaning of there being no expiation for each of these five? And what are examples of other major sins for which expiation is beneficial but were not mentioned in the hadith?

The Hadith (definition) "Five deeds for which there is no expiation..." is interpreted to mean that righteous deeds do not expiate major sins. Rather, major sins are purified through sincere repentance (Tawbah (definition) Nasuh) and seeking forgiveness, or by the prescribed punishment (Hadd) if applicable, or by God's forgiveness. Expiation through repentance and legal punishment is established by Quranic and Prophetic texts. God has promised to accept the repentance of His believing servants, to forgive the sins of disbelievers if they desist, and to transform the evil deeds of repentant individuals into good deeds. Likewise, the Hadith of 'Ubadah ibn al-Samit indicates that the enforcement of a legal punishment serves as an expiation for the perpetrator of a major sin, even if he has not repented, and this is the view of the majority of scholars. As for one who performs sincere repentance, God accepts it, and no accountability remains upon him. However, if someone dies having committed a major sin without repenting from it, he is under the Will of God.