In his Khutbah recorded in Nahj-Al Balaghah # 216, Ali RA Said:
فلا تكفوا عن مقالة بحق ، أو بعدل مشورة ، فإني لست في نفسي بفوق أن أخطىء ، ولا آمن ذلك من فعلي
“Do not evade me as the people of passion are (to be) evaded, do not meet me with flattery and do not think that I shall take it ill if a true thing is said to me, because the person who feels disgusted when truth is said to him or a just matter is placed before him would find it more difficult to act upon them. Don’t stop saying the Truth, or Just Advice, As I am not above making Mistakes, and I am not safe from making Mistakes in my Actions”.
Source: Nahjul Balagha, Sermon 216.