899
Musnad Ahmedlt was narrated from Abu Umamah that
"Ali bin Abi Talib (رضي الله عنه) told him that he used to go to the Prophet (ﷺ). He said: If I found him praying, he would say tasbeeh and I would enter, and if he was not praying, he would give me permission to enter.
Reference: Musnad Ahmad 899
Arabic/English book : Book 5, Hadith 899
Arabic/English book : Book 5, Hadith 899