Al-Adab Al-Mufrad
Behaviour with people
كتاب تعامل الناس
Chapter 9: Two should not converse to the exclusion of a third
'Abdullah reported that the Messenger of Allah, may Allah bless him and grant him peace, said, "When there are three people, two should not converse together to the exclusion of the third."
Chapter 10: When there are four people
Chapter 11: When someone sits without someone else, he should ask his permission to leave
Abu Burda ibn Abi Musa said, "I sat with 'Abdullah ibn Sallam. He said, 'You have sat down with us, but now it is time for us to leave.' I said, 'If you like.' He got up and I followed him to the door."