Sahih Bukhari
Military Expeditions led by the Prophet (pbuh) (Al-Maghaazi)
Volume: 005 / Book Number: 059 / Hadith Number: 497
Narrated 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.