People say that Ibn Umar accepted Islam before Umar, but that is not the case. What actually happened was that on the day of Hudaybiyyah, Umar sent Abdullah to fetch a horse of his that was with a man from the Ansar, so he could come and fight on it. Meanwhile, the Messenger of Allah ﷺ was taking the pledge from people under the tree, and Umar was unaware of this. Abdullah gave his pledge, then went to fetch the horse and brought it to Umar, who was putting on his armor for battle. Abdullah informed him that the Messenger of Allah ﷺ was taking the pledge under the tree.Umar said, "Let us go," and went with him until he gave his pledge to the Messenger of Allah ﷺ. This is the incident that has led people to say that Ibn Umar accepted Islam before Umar.
حدثني شجاع بن الوليد سمع النضر بن محمد حدثنا صخر
إن الناس يتحدثون أن ابن عمر أسلم قبل عمر وليس كذلك ولكن عمر يوم الحديبية أرسل عبد الله إلى فرس له عند رجل من الأنصار يأتي به ليقاتل عليه ورسول الله ﷺ يبايع عند الشجرة وعمر لا يدري بذلك فبايعه عبد الله ثم ذهب إلى الفرس فجاء به إلى عمر وعمر يستلئم للقتال فأخبره أن رسول الله ﷺ يبايع تحت الشجرة قال فانطلق فذهب معه حتى بايع رسول الله ﷺ فهي التي يتحدث الناس أن ابن عمر أسلم قبل عمر