'I have not profited by any speech after the Messenger of Allah (SAWA) more than by a letter written by 'Ali b. Abi Talib (AS). He wrote to me, saying, But now, indeed man grieves for having missed that which he would not have attained anyway, and is overjoyed at attaining that which he would not have missed anyway. So, let your happiness be for what you attain for your Hereafter, and let your regret be for what you miss of it. Do not be happy for what you attain for this world, nor regret sorrowfully what you miss from it, and let your concern be for what comes after death, and peace be with you. '