Sunan al-Nasa'i The Book of Forgetfulness (In Prayer) al-Qasim bin Zakaria bin Dinar القاسم بن زكريا بن دينار القرشي Hammad bin Usamah حماد بن أسامة - أبو أسامة Shrhbyl bin Mdrk al-J'fy شرحبيل بن مدرك الجعفي الكوفي “I had certain times when I used to come to the Messenger of Allah (ﷺ). When I came to him I would ask for permission to enter. If I found him praying he would clear his throat and I would enter, and if I found him free he would give me permission (to enter).” https://parallelquran.com/hadith/sunan-al-nasai-1213/