Abdullah bin Umar set out to perform Umrah during the time of the civil strife and said, "If I am prevented from reaching the House, we will do as we did with the Messenger of Allah ﷺ." So he entered the state of ihram for Umrah, because the Messenger of Allah ﷺ had entered ihram for Umrah in the year of Hudaybiyyah.
أن عبد الله بن عمر خرج معتمرا في الفتنة، فقال: إن صددت عن البيت صنعنا كما صنعنا مع رسول الله ﷺ، فأهل بعمرة من أجل أن رسول الله ﷺ لو كان أهل بعمرة عام الحديبية.
Malik narrated it in Hajj (103) from Nafi, who said, and he related it.Bukhari also narrated it in Maghazi (4183), and Muslim in Hajj (1230:180), both of them by way of Malik with the same chain.