A riddle he put to them
Ibn Umar knew the answer and was too young to say it.
إِنَّ مِنَ الشَّجَرِ شَجَرَةً لاَ يَسْقُطُ وَرَقُهَا، وَإِنَّهَا مَثَلُ الْمُسْلِمِ، فَحَدِّثُونِي مَا هِيَ
Inna mina-sh-shajari shajaratan lā yasquṭu waraquhā, wa innahā mathalu-l-muslim, fa-ḥaddithūnī mā hiya
“Among the trees there is a tree whose leaves do not fall. It is like the Muslim. Tell me what it is.”
Where this comes from
They started guessing at the desert trees. Ibn Umar says it occurred to him that it was the date palm, and he was embarrassed to speak in front of the older men. Afterwards he told his father, who said he would rather Ibn Umar had said it than have such and such.
The full narration
Narrated Ibn `Umar:Allah's Messenger (ﷺ) 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 Messenger (ﷺ) ?" He replied, "It is the date-palm tree
Source
Ṣaḥīḥ al-Bukhārī · 61
- Agreed upon as authentic (al-Bukhārī / Muslim)