The Messenger of Allah ﷺ said: "When you perform Wudu', do so properly, and wash in between the fingers (Al-Asabi')."[2] [1] Al-Asabi' is plural meaning fingers as well as toes, and the author mentioned only one narration on the topic whereas some of them clarify "of the hands and feet." So he mentioned the general wording amids chapters how to wash the feet. [2] Part of this narration preceded under No. 87. (Using translation from Nasāʾī 114)  

قَالَ رَسُولُ اللهِ ﷺ «إِذَا تَوَضَّأْتَ فَأَسْبَغِ الْوُضُوءَ وَخَلِّلْ بَيْنَ الْأَصَابِعِ»