How long was the Berds(darhi) of Holy Prophet (P.B.U.H)?I mean what is the sunnat about this.

Assalaam alaikum,

This should help you...
Islam Question and Answer - Doubts about the obligation to let the beard grow and answers to them (http://www.islamqa.com/en/ref/75525/Beard%20Sunnah)

Islam Question and Answer - Is there any recommended length of the beard? (http://www.islamqa.com/en/ref/6657/Beard%20Sunnah)

Wa alaikum salaam