"There was a man among the Ansar who would sit with the Messenger of Allah ﷺ, and he would listen to the Ahadith of the Prophet ﷺ and he was amazed with them but he could not remember them. So he complained about that to the Messenger of Allah ﷺ. He said: 'O Messenger of Allah! I listen to your Ahadith and I am amazed but I can not remember them.' So the Messenger of Allah ﷺ said: 'Help yourself with your right hand' and he motioned with his hand as if writing.'"  

كَانَ رَجُلٌ مِنَ الأَنْصَارِ يَجْلِسُ إِلَى النَّبِيِّ ﷺ فَيَسْمَعُ مِنَ النَّبِيِّ ﷺ الْحَدِيثَ فَيُعْجِبُهُ وَلاَ يَحْفَظُهُ فَشَكَا ذَلِكَ إِلَى النَّبِيِّ ﷺ فَقَالَ يَا رَسُولَ اللَّهِ إِنِّي أَسْمَعُ مِنْكَ الْحَدِيثَ فَيُعْجِبُنِي وَلاَ أَحْفَظُهُ فَقَالَ رَسُولُ اللَّهِ ﷺ اسْتَعِنْ بِيَمِينِكَ وَأَوْمَأَ بِيَدِهِ لِلْخَطِّ وَفِي الْبَابِ عَنْ عَبْدِ اللَّهِ بْنِ عَمْرٍو