Hadith 17:527
Yazid ibn Harun narrated to us, from al-Jurayri, from Ibn Buraydah, who said: A man sought permission to enter from a man among the companions of the Prophet, may Allah bless him and grant him peace, while he was standing at the door. He said, "May I enter?" three times, while he was looking at him, but he did not give him permission. Then he said, "Peace be upon you, may I enter?" He said, "Enter." Then he said, "If you were to stand until the night saying 'May I enter?', I would not have given you permission until you began with the greeting."
حدثنا يزيد بن هارون عن الجريري عن بن بريدة قال استأذن رجل على رجل من أصحاب النبي صلى الله عليه وسلم وهو قائم على الباب فقال أأدخل ثلاث مرات وهو ينظر إليه فلم يأذن له ثم قال السلام عليكم أأدخل فقال ادخل ثم قال لو قمت إلى الليل تقول أأدخل ما أذنت لك حتى تبدأ بالسلام