Hadith 229
“I asked Ibn ‘Abbas رضي الله عنه, 'Does one ask permission of one's sister ?' He replied, 'Yes.' I repeated it and said, 'My two sisters live in my room and I provide for them and spend on them, so do I ask them for permission?' He said, 'Yes. Do you want to see them naked?' …”
to get into the room
Ata' (رضي الله عنه)Al-Adab Al-Mufrad 1063Adab & Virtues of Asking Permission