Is it permissible to atone for the sin of wrongfully killing a soul by means other than fasting for sixty consecutive days due to an inability to do so, provided that blood money is paid and the poor are fed?

The person who kills by mistake is obliged to pay the blood money (Diyyah) and offer expiation (Kaffarah). The blood money has already been paid. As for the expiation, it is the freeing of a believing slave. If one cannot find a slave to free, then one must fast for two consecutive months. This fasting is obligatory upon your companion unless he is genuinely unable to do so. The usual difficulty of fasting does not negate its obligation. The issue of a person unable to fast moving to feeding sixty poor people is a matter of disagreement among jurists.