Al-Khaleel bin Ahmad (May Allah have mercy on him) said,

“ما سمعت شيئًا إلا كتبته ، ولا كتبت شيئا إلا حفظته ، ولا حفظت شيئا إلا انتفعت به”

“I did not hear anything except that I wrote it down, and I did not write anything down except that I memorized it, and there was not anything that I memorized except that I benefited from it.”

Taken from: Jaami’ bayaan ilm wa fadlihi under the chapter, “Dhakara rukhsah fee kitaabil ilm”

جامع بيان العلم وفضله لابن عبد البر: باب ذكر الرخصة في كتاب العلم