Ibn Umar witnessed the Conquest at the age of twenty, having with him a stubborn horse and a heavy spear. Ibn Umar went out to gather fodder for his horse, and the Messenger of Allah ﷺ said, "Indeed Abdullah, indeed Abdullah."
شهد ابن عمر الفتح وهو ابن عشرين سنة، ومعه فرس حرون ورمح ثقيل، فذهب ابن عمر يختلي لفرسه، فقال رسول الله ﷺ: إن عبد الله، إن عبد الله.
Ahmad narrated it (4600) from Sufyan (that is, Ibn Uyayna), from Ibn Abu Najeeh (that is, Abdullah), from Mujahid, who related it. Its chain of transmission is sahih. Mujahid's statement should be understood as meaning that he heard this from Ibn Umar, given his long companionship with him, for he had heard many hadiths from him. This is supported by the fact that Ibn Hajar mentioned this hadith under the entry for Mujahid, narrating from Ibn Umar, in Ithaf Mahra. Allah knows best.As for Haythami, he faulted it for being disconnected, after attributing it to Tabarani (6/346).His statement, "Indeed Abdullah, indeed Abdullah," refers to a righteous man, as mentioned in a sahih hadith, even though this exact wording is not established in this hadith. The publisher of Majma al-Zawaid added this addition from Shadharat Dhahab, so perhaps the author of Shadharat Dhahab intended it as an explanation rather than as the actual text.