It is narrated from Qays bin Abi Hazim that he said: I was in Madinah, going around the market, when I reached the place called "Ahjar al-Zayt", and I saw a crowd of people gathered around a horseman who was reviling Sayyiduna Ali bin Abi Talib (may Allah be pleased with him), while the people stood around him listening. Just then Sayyiduna Sa'd bin Abi Waqqas (may Allah be pleased with him) arrived, stood by them and asked: "What is going on?" The people said: "This man is reviling Ali bin Abi Talib." So Sayyiduna Sa'd (may Allah be pleased with him) went forward, and the people made way for him until he stood in front of that man, and he said: "O you! On what basis do you revile Ali bin Abi Talib? Was he not the first to accept Islam? Was he not the first person to pray with the Messenger of Allah (peace and blessings be upon him)? Was he not the most abstinent of people? Was he not the most knowledgeable of people?" He went on mentioning the virtues of Sayyiduna Ali (may Allah be pleased with him) until he said: "Was he not the son-in-law of the Messenger of Allah (peace and blessings be upon him), the husband of his daughter? Was he not the standard-bearer of the Messenger of Allah (peace and blessings be upon him) in the battles?" Then Sayyiduna Sa'd (may Allah be pleased with him) turned towards the Qiblah, raised his hands and supplicated: "O Allah, this man is reviling one of Your friends (awliya'), so show these people a sign of Your power before this crowd disperses." Qays says: By Allah, we had not yet dispersed when his mount threw him down, and he fell on his head onto those stones, so that his skull split open and he died on the spot. This hadith is sahih (authentic) on the condition of the two Shaykhs (Bukhari and Muslim).