What is the ruling of Islamic law regarding someone who neglected to give their mother her medication, leading to her death a month later? Does this necessitate an expiatory fast like that for accidental killing, and what is Allah's punishment for him?

Negligence in treating a mother and not giving her medication, leading to her death, is a grave error and contrary to filial piety. There is no blame for forgetfulness, but negligence is blameworthy. The necessity of expiation and indemnity depends on several details: If the mother was able to take the medication herself, or if the cause of death was not the failure to take the medication, then there is no indemnity on him. However, if it is certain or highly probable that the cause of death was the failure to take the medication, and the mother was unable to take it herself, and he was responsible for giving her the medication, then he is liable for indemnity and expiation. Her blood money is on his 'aqila (male relatives on the father's side), and he inherits nothing from her. His punishment with Allah is unseen, and repentance, supplication, charity, and kindness to relatives and friends are beneficial for him.