Sahih al-Bukhari 61

Qutayba narrated to us. Ismail ibn Ja'far narrated to us, from Abdullah ibn Dinar, from Ibn Umar, who said: The Messenger of Allah (peace and blessings be upon him) said: ‘Among the trees there is a tree whose leaves do not fall, and it is like a Muslim. Tell me, what is it?’ The people began naming the trees of the open country. Abdullah said: It occurred to me that it was the date palm, but I felt shy. Then they said: ‘Tell us what it is, Messenger of Allah.’ He said: ‘It is the date palm.’