Behold, as for those who are bent on denying the truth and die as deniers of the truth -their due is rejection by God, and by the angels,, and by all [righteous] men.
Al-Baqara (The Cow) Verse 161
Whenever the Prophet 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.
Sahih Bukhari: Volume 1, Book 3, Number 94