Silsilat al-Ahadith al-Sahihah

A man from the tribe of Banu Amir narrates that he sought permission from the Prophet Muhammad (peace be upon him) by saying: "May I come in?" The Prophet (peace be upon him) instructed his servant, saying: "The manner in which this man is seeking permission is not good, so go to him and tell him that he should seek permission by saying: 'As-salamu alaikum, may I come in?'"