Sahih Bukhari Volume 9, Book 93, Hadith Number 558.

Narrated By Abu Huraira : Allah’s Apostle said, “The example of a believer is that of a fresh green plant the leaves of which move in whatever direction the wind forces them to move and when the wind becomes still, it stand straight. Such is the similitude of the believer: He is disturbed by calamities (but is like the fresh plant he regains his normal state soon). And the example of a disbeliever is that of a pine tree (which remains) hard and straight till Allah cuts it down when He will.” (See Hadith No. 546 and 547, Vol. 7).