Ruling on killing someone by mistake and making no Kaffarah at the time and now being unable to make Kaffarah

Q: A Muslim person is obliged to offer Kaffarah (expiation) for killing. Scholars have obliged him to observe Sawm (Fast) for two consecutive months. Yet he says that he cannot observe Sawm consecutively since this is too hard for him, because he practices some military activities continually. Is it permissible for him to refrain from observing Sawm and feed poor people due to his circumstances?

A: He who kills a believer by mistake should emancipate a believing slave. If he finds this beyond his means, then he should observe Sawm for two consecutive months. If he still finds this beyond his means, then he will continue to be excused and exempted until he can either emancipate a believing slave or observe Sawm for two consecutive months until his death. To put it in other words, if he died without being able to do so, he will be exempted In sha’a-Allah (if Allah wills). It is not permissible to feed poor people instead of observing Sawm according to the sound opinion since Allah did not mention this regarding the Kaffarah (Part No. 21; Page No. 291) for involuntary manslaughter whereas He (Exalted be He) mentioned it regarding other types of Kaffarah. Indeed "never is your Lord forgetful". It is not valid to use Qiyas (analogy) to apply the ruling on a certain Kaffarah to another one since Kaffarah is among the acts of worship that are Tawqifiy (bound by a religious text and not amenable to personal opinion).May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.