A man from the Ansar used to sit with the Prophet ﷺ and listen to his words. The hadith would impress him, but he could not remember it. He complained about this to the Prophet ﷺ, saying, "Messenger of Allah, I hear hadith from you and they impress me, but I cannot retain them."The Messenger of Allah ﷺ replied, "Seek the help of your right hand," and he gestured with his hand to indicate writing.
حدثنا قتيبة حدثنا الليث عن الخليل بن مرة عن يحيى بن أبي صالح
كان رجل من الأنصار يجلس إلى النبي ﷺ فيسمع من النبي ﷺ الحديث فيعجبه ولا يحفظه فشكا ذلك إلى النبي ﷺ فقال يا رسول الله إني أسمع منك الحديث فيعجبني ولا أحفظه فقال رسول الله ﷺ استعن بيمينك وأومأ بيده للخط
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Its isnad is daif. Ibn Adi narrated it in 1/36 through Khalil bin Murra from him, and he is daif (Taqrib), while Yahya bin Abu Salih is majhul (also).There is also a report on this topic from Abdullah bin Amr [Abu Dawud, no. 3646].