Musnad Ahmad 5:715

Abdullah narrated to us, Muhammad ibn Sulayman Lawin narrated to me, Muhammad ibn Jabir narrated to us, from Simak, from Hanash, from Ali ibn Abi Talib, who said: The Prophet, peace and blessings of Allah be upon him, sent me as a judge to Yemen. He then mentioned the hadith and said: "Indeed, Allah will make your heart firm and guide your intellect." He then mentioned the rest of the hadith.