Musnad Ahmad 27:152

Sufyan narrated to us, from Ibn Abi Najih, from Mujahid, who said: I accompanied Ibn Umar to Medina, and I did not hear him narrate from the Prophet, may Allah bless him and grant him peace, except for one hadith. We were with the Prophet, may Allah bless him and grant him peace, when a *jumara* (the heart of a palm tree) was brought. He said: "Indeed, among the trees, there is a tree whose likeness is like the likeness of the Muslim man." I wanted to say: "It is the date palm," but I looked and saw that I was the youngest of the people, so I remained silent. Then the Messenger of Allah, may Allah bless him and grant him peace, said: "It is the date palm."