Sahih Bukhari Volume 1, Book 3, Hadith 61

حَدَّثَنَا قُتَيْبَةُ، حَدَّثَنَا إِسْمَاعِيلُ بْنُ جَعْفَرٍ، عَنْ عَبْدِ اللَّهِ بْنِ دِينَارٍ، عَنِ ابْنِ عُمَرَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ إِنَّ مِنَ الشَّجَرِ شَجَرَةً لاَ يَسْقُطُ وَرَقُهَا، وَإِنَّهَا مَثَلُ الْمُسْلِمِ، فَحَدِّثُونِي مَا هِيَ ‏"‏‏.‏ فَوَقَعَ النَّاسُ فِي شَجَرِ الْبَوَادِي‏.‏ قَالَ عَبْدُ اللَّهِ وَوَقَعَ فِي نَفْسِي أَنَّهَا النَّخْلَةُ، فَاسْتَحْيَيْتُ ثُمَّ قَالُوا حَدِّثْنَا مَا هِيَ يَا رَسُولَ اللَّهِ؟ قَالَ ‏"‏ هِيَ النَّخْلَةُ "

Narrated By 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 tree."