सहीह अल-बुखारी #94
Sahih (Authentic)
Whenever the Prophet (ﷺ) asked permission to enter, he knocked the door thrice with greeting and whenever he spoke a sentence (said a thing) he used to repeat it thrice. (See Hadith No. 261, Vol)
वर्णन की श्रृंखला (इस्नाद)
Narrated Anas