It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) said to Ali (may Allah be pleased with him): "You are to me in the position that Harun was to Musa (peace be upon them both)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11041