Is the impermissibility of having intercourse with one's wife specific only to a person fasting as an expiation for ẓihār, or does it include someone who fasts for sixty days as an expiation for unintentional killing?

Sexual intercourse with one's wife is only forbidden for a man who is fasting as expiation for ẓihār. As for one who is obligated to perform other types of fasting expiation, it is not forbidden, because the fast's domain is the day, not the night. The one who performs ẓihār has his wife forbidden to him until he expiates, based on Allah's saying: ﴿Those who declare ẓihār against their wives and then wish to go back on what they said, [the penalty] is the freeing of a slave before they touch each other. This is an admonition for you, and Allah is All-Aware of what you do.﴾ Intercourse with one's wife at night, for one who has not performed ẓihār, does not break the continuity of the fast, nor does intercourse during the day due to forgetfulness or for a permissible excuse that allows breaking the fast.