حَدَّثَنَا عُثْمَانُ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا شَرِيكٌ، عَنْ أَبِي الْحَسْنَاءِ، عَنِ الْحَكَمِ، عَنْ حَنَشٍ، قَالَ رَأَيْتُ عَلِيًّا يُضَحِّي بِكَبْشَيْنِ فَقُلْتُ مَا هَذَا فَقَالَ إِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم أَوْصَانِي أَنْ أُضَحِّيَ عَنْهُ فَأَنَا أُضَحِّي عَنْهُ ‏.‏

Narrated Hanash: I saw Ali sacrificing two rams; so I asked him: What is this? He replied. The Messenger of Allah (PBUH) enjoined upon me to sacrifice on his behalf, so that is what I am doing. Translation Not Available

Book reference: Sunan Abi Dawud Book 16 Hadith 2790
Web reference: Sunan Abi Dawud Book 15 Hadith 2784