Sahih Bukhari | Volume 3 | Hadith Number 33

Narrated by Nafi
When Abdullah bin Umar set out for Mecca intending to perform Umra, at the time of afflictions, he said, "If I should be prevented from reaching the Kaba, then I would do the same as Allah's Apostle did, so I assume the Ihram for Umra as Allah's Apostle assumed the Ihram for Umra in the year of Hudaibiya."