Sahih Bukhari Volume 001, Book 003, Hadith Number 059.
Narated By Ibn 'Umar : The Prophet said, "Amongst the trees, there is a tree, the leaves of which do not fall and is like a Muslim. Tell me the name of that tree." Everybody started thinking about the trees of the desert areas. And I thought of the date-palm tree. The others then asked, "Please inform us what is that tree, O Allah's Apostle?" He replied, "It is the date-palm tree."