كتاب الطهارة
Read the English translation first, with the original Arabic directly underneath.
It was narrated from 'Asim bin Laqit that his father said:
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.
إِذَا تَوَضَّأْتَ فَأَسْبِغِ الْوُضُوءَ وَخَلِّلْ بَيْنَ الأَصَابِعِ