What is the ruling on a conditional vow, and is expiation obligatory if its fulfillment becomes impossible, and is it permissible to be released from it with expiation merely due to difficulty?

Whoever vows obedience to Allah must fulfill their vow, for Allah Almighty says: (And let them fulfill their vows), and because the Prophet, peace and blessings be upon him, said: "Whoever vows to obey Allah, let him obey Him." If fulfilling the vow becomes impossible, it is nullified, and an expiation for breaking an oath becomes obligatory, for the Prophet, peace and blessings be upon him, said: "The expiation for a vow is the expiation for an oath." This expiation is: freeing a slave, or feeding ten poor people, or clothing them; and whoever cannot find [any of these] should fast for three days. It is not permissible to be released from a vow merely due to difficulty, without it becoming impossible or unattainable.