Sahih Bukhari, Chapter: Knowledge

I said to Allah's Apostle "I hear many narrations (Hadiths) from you but I forget them." Allah's Apostle said, "Spread your Rida' (garment)." I did accordingly and then he moved his hands as if filling them with something (and emptied them in my Rida') and then said, "Take and wrap this sheet over your body." I did it and after that I never forgot any thing.