Asking Permission

Bukhari :: Book 8 :: Volume 74 :: Hadith 263

Narrated Abu Huraira:

I entered (the house) along with Allah's Apostle . There he found milk in a basin. He said, "O Abu Hirr! Go and call the people of Suffa to me." I went to them and invited them. They came and asked permission to enter, and when it was given, they entered. (See Hadith No. 459 for details)