Is leaving a will obligatory so much so that one could be sinful if they do not do it?

Answer

If the person keeps other’s belongings, owes something to somebody or he should perform some missed rituals (missed prayers, fasts, khums, zakat, kaffārah, maẓālim, haj), of which they could not discharge their responsibility, it is obligatory for them to leave a will. Otherwise, it is not obligatory.