Is a mother obligated to fast for two consecutive months, believing that she accidentally killed her infant, and is the husband sinful for interrupting this fast with intercourse?

It appears that there is no expiation required of the woman, because doctors have determined that the child's death was sudden. There is also no sin upon her husband if he had intercourse with her while she was fasting, due to the Prophet's (peace be upon him) saying: "It is not permissible for a woman to fast while her husband is present except with his permission." She should be treated kindly and with gentleness, taking her circumstances into consideration after her affliction.