Qutbah bin Malik narrates: One of the governors reviled Sayyiduna Ali (may Allah be pleased with him), so Sayyiduna Zayd bin Arqam (may Allah be pleased with him) stood up towards him and said: "Listen! I know well that the Messenger of Allah (peace and blessings be upon him) forbade reviling the dead, so why do you revile Ali when he has passed away?"
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 4954