Is it permissible to offer a sacrifice on behalf of the Prophet (PBUH), and what is the ruling on the Hadith of Ali (may Allah be pleased with him): "He used to sacrifice two rams, one on behalf of the Prophet (PBUH) and the other on behalf of himself. When he was asked about it, he said: 'He – meaning the Prophet (PBUH) – commanded me to do so, and I will never abandon it'"?

No one is permitted to sacrifice on behalf of the Prophet, peace and blessings be upon him, and the fundamental principle in acts of worship is prohibition unless proven otherwise. The narration transmitted from Ali, may Allah be pleased with him, stating that he used to sacrifice two rams, one on behalf of the Prophet, peace and blessings be upon him, and the other on behalf of himself, citing the Prophet's instruction to him in this regard, has a weak chain of transmission. This is due to the poor memory of Shareek, the weakness of Hanash, and the unknown status of Abu Al-Hasna. If the weakness of the hadith is established, then the principle remains that sacrificing on behalf of the Prophet, peace and blessings be upon him, is not permissible. When sacrificing, a Muslim sacrifices on behalf of himself and his household, both living and deceased, with the deceased included dependently. As for sacrificing specifically on behalf of a deceased person without a will, there is no evidence to support it.