Musnad Ahmad 27:1496

Aswad narrated to us, Sharik narrated to us, I heard Salamah ibn Kuhayl mentioning from Mujahid, from Ibn Umar, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "I truly know of a tree that is beneficial, like the believer; it is the one whose leaves do not fall." Ibn Umar said: I wanted to say it is the date palm, but I was afraid because of my age. Then I heard him (the Prophet) say afterwards: "It is the date palm."