Hadith 952
ان رسول الله صلى الله عليه وسلم أوصانى أن أضحى عنه فأنا أضحى عنه
"(Sayyiduna Ali, may Allah be pleased with him, said that) the Messenger of Allah, peace and blessings be upon him, advised me to offer a sacrifice on his behalf, so I offer a sacrifice on his behalf."