SAHIH BUKHARI

Volume 1, Book 3, Number 59, 60, 61, 62:

Narrated 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 Al - lah's Apostle?" He replied, "It is the date-palm tree."