Assalaamu alaykum. If a father kills his son, he is obliged to pay the Diyyah (blood money), but if he is poor and his relatives are also poor and they are unable to pay it, then what will the punishment be in this situation? I know that this is a silly question, but I want to know please.

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

The Diyah differs based on the type of murder. If a father deliberately killed his son (premeditated murder), the Diyah should be paid from the father's wealth only. If the father is poor, he should be given respite until he becomes able to pay it. In the case of an accidental murder and in case the father is poor, the ‘Aaqilah (paternal male relatives) of the father are required to pay the Diyah on his behalf to the heirs of the son, and the father is not one of the heirs in this case. If the ‘Aaqilah are poor as well and cannot pay the Diyah, it should be paid from the Public Treasury. The Kuwaiti Encyclopedia of Fiqh states, "The scholars underlined that if the murderer has no ‘Aaqilah or his ‘Aaqilah are unable to pay the Diyah of the accidental murder or the remaining part of the Diyah (if he or she is able to pay only part of the Diyah), then the Diyah should be paid from the Public Treasury. The Prophet, sallallaahu ‘alayhi wa sallam, said, 'I am the heir of the one who has no heir; I will pay the blood money on his behalf and inherit from him.'"

Allah knows best.