BELIEVE in God and His Apostle, and spend on others out of that of which He has made you trustees: or, those of you who have attained to faith and who spend freely [in God’s cause] shall have a great reward.
Al-Hadid (Iron) Verse 7
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