What is the ruling on the statement of one who says: "By Allah—I swear—if I do this thing, then Allah will cause me to abide eternally therein" or "By Allah, a promise," and is an expiation required of him?

It is not permissible to invoke evil upon oneself or to pray for eternal damnation in Hell, due to the prohibition of the Prophet, peace and blessings be upon him, regarding such actions. This type of speech is not considered a legal oath, and the majority of jurists hold that it does not necessitate an expiation for an oath.