The first line isn't by al-Imaam ash-Shaafi'ee (rahimahullaahu ta'aala), it's from another poets sayings etc that I'd just like to post because it's meaningful and what you're asking for follows it bi'ithnillaahi ta'aala..............
وما سُمي الإنسان إلا لنسيه ** ولا القلب إلا أنه يتقلبWa Maa Summiyaa al-Insaanu Illa Linasyeehi -- Wa Laa Qalbun Illa Annahu Yataqallabu“He's only called man cause of his forgetfulness, and it is only called the heart cause it changes so rapidly.”
شكوت إلى وكيع سوء حفظي** فأرشدني إلى ترك المعاصيوقــال إن علم الله نـــــــورٌ ** ونور الله لا يعطى لعاصي
Shakawtu Ilaa Wakee` Soo'a Hifdhee -- Fa-arshadanee Ilaa Tark al-Ma`aasee Wa Qaala Inna `Ilma Allaahi Noorun -- Wa Nooru Allaahi La Yu`taa Li `Aasee
“I complained to Wakee` about my bad memory, and he taught me that I should keep away from sin.He said that knowledge of Allaah is light, and the light of Allaah is not given to the sinner.”