Is it permissible for a person to pray for death upon himself every night because he swore an oath by God to do so and what he swore to happened, and is expiation (kaffarah) obligatory upon him if his action is impermissible?

It is not permissible for a person to supplicate against themselves for death or any evil, due to the prohibition of the Prophet, peace and blessings be upon him, regarding that, and because the angels say "Amen" to what is said. And whoever swears that they will supplicate against themselves if a certain matter occurs, this is an oath to commit a sin, and they must break their oath and offer expiation for it, because fulfilling an oath to commit a sin is not permissible; rather, expiation is obligatory in such a case.