(1) باب إِذَا أُحْصِرَ الْمُعْتَمِرُ
Narrated 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 Ka`ba, then I would do the same as Allah's Messenger (ﷺ) did, so I assume the lhram for Umra as Allah's Messenger (ﷺ) assumed the Ihram for Umra in the year of Hudaibiya."
Reference: Sahih al-Bukhari 1806
In-book reference: Book 27, Hadith 1
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 3, Book 28, Hadith 33