Sahih Muslim Book 39, Hadith Number 6747.

‘Abdullah b. Umar reported that Allah’s Messenger (may peace be upon him) said: There is a tree amongst trees, the leaves of which do not wither and that is like a Muslim; tell me which that (tree) can be? The people began to think of the trees of the forest. Abdullah said: I thought that it could be the date-palm tree, but I felt hesitant (to say that). They (the Companions) then said: Allah’s Messenger, (kindly) tell us which that can be? Thereupon he said: It is the date-palm tree. I made a mention of that to ‘Umar, whereupon he said: Had you said that it meant the date-palm tree, this statement of yours (would have been dearer to me) than such and such things.