Mishkat al-Masabih, hadith 1384

وَعَنْ حَنَشٍ قَالَ: رَأَيْتُ عَلِيًّا رَضِيَ اللَّهُ عَنْهُ يُضَحِّي بِكَبْشَيْنِ فَقُلْتُ لَهُ: مَا هَذَا؟ فَقَالَ: (إِنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أَوْصَانِي أَنْ أُضَحِّيَ عَنْهُ فَأَنَا أُضَحِّي عَنْهُ. رَوَاهُ أَبُو دَاوُدَ وَرَوَى التِّرْمِذِيُّ نَحْوَهُ

I saw Ali sacrificing two rams and asked him the meaning of it. He replied, “God’s Messenger enjoined me to sacrifice on his behalf, so that is what I am doing.” Abu Dawud transmitted it, and Tirmidhi transmitted something similar.