Narrated Ibn `Umar: Allah's Apostle 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 but felt shy to answer the others then
asked, "What is that tree, O Allah's Apostle ?" He replied,
"It is the date−palm true."
(Sahih Bukhari in chapter Book of Knowledge kitabul ilm)