Sahih Bukhari Volume 5, Book 59, Hadith Number 497.

Narrated By Nafi : Abdullah bin Umar set out for Umra during the period of afflictions, and he said, “If I should be stopped from visiting the Kaba, I will do what we did when we were with Allah’s Apostle.” He assumed Ihram for ‘Umra in the year of Al-Hudaibiya.