Knocking 3 times
Abu Saeed Khudri (R.A) narrates, Abu Musa once came to me and said that, Umar (R.A) had called for me, I came to the door and proclaimed (Arabic) 3 times Umar (R.A) didn’t reply. Therefore I returned (thereafter when Umar (R.A) Abu Musa (R.A)) he said what kept you from visiting me? I replied Indeed I came and I gave salam 3 times you didn’t reply so I returned and verily Rasulullah (S.A.W) once said to me “when one of you asks for permission 3 times and doesn’t receive an answer then he must return!
(After hearing this) Umar (R.A) said bring me evidence on what you say!! Abu Saeed Khudri (the narrator) said “therefore stood up and went with him (Abu Musa) to Umar (R.A) and gave evidence (for what Abu Musa had said)
To stand on the right /left of door
Abdullah ibne Busr (R.A) once narrated that whenever Rasulullah (S.A.W) came by a door he never stood in front of the door, rather he would stand on the right or the left. Then he would say (Arabic) that was because in those days doors never had any veils.
Abu Saeed Khudri narrated that Rasullilah (S.A.W) said “When there are three ‘3’ persons on a journey then make one amongst them the Ameer.