Sahih Bukhari

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."

That Ubaidullah bin `Abdullah and Salim bin `Abdullah informed him that they told Ibn `Umar when Ibn Az-Zubair was attacked by the army, saying "There is no harm for you if you did not perform Hajj this year. We are afraid that you may be prevented from reaching the Ka`ba." Ibn `Umar said "We set out with Allah's Messenger (ﷺ) and the non-believers of Quraish prevented us from reaching the Ka`ba, and so the Prophet (ﷺ) slaughtered his Hadi and got his head shaved." Ibn `Umar added, "I make you witnesses that I have made `Umra obligatory for me. And, Allah willing, I will go and then if the way to Ka`ba is clear, I will perform the Tawaf, but if I am prevented from going to the Ka`ba then I will do the same as the Prophet (ﷺ) did while I was in his company." Ibn `Umar then assumed Ihram for Umra from Dhul-Hulaifa and proceeded for a while and said, "The conditions of `Umra and Hajj are similar and I make you witnesses that I have made `Umra and Hajj obligatory for myself." So, he did not finish the Ihram till the day of Nahr (slaughtering) came, and he slaughtered his Hadi. He used to say, "I will not finish the Ihram till I perform the Tawaf, one Tawaf on the day of entering Mecca (i.e. of Safa and Marwa for both `Umra and Hajj).

Some of the sons of `Abdullah told him (i.e. `Abdullah) if he had stayed (and not performed Hajj that year).

Allah's Messenger (ﷺ) was prevented from performing (`Umra) Therefore, he shaved his head and had sexual relations with his wives and slaughtered his Hadi and performed Umra in the following year.

(Abdullah) bin `Umar used to say, "Is not (the following of) the tradition of Allah's Messenger (ﷺ) sufficient for you? If anyone of you is prevented from performing Hajj, he should perform the Tawaf of the Ka`ba and between As-Safa and Al-Marwa and then finish the Ihram and everything will become legal for him which was illegal for him (during the state of Ihram) and he can perform Hajj in a following year and he should slaughter a Hadi or fast in case he cannot afford the Hadi."

Allah's Messenger (ﷺ) slaughtered (the Hadi) before he had his head shaved and then he ordered his Companions to do the same.

That `Abdullah and Salim said to `Abdullah bin `Umar, "(You should not go for Hajj this year)." `Abdullah bin `Umar replied, "We set out with the Prophet (to Mecca for performing `Umra) and the infidels of Quraish prevented us from reaching the Ka`ba. Allah's Messenger (ﷺ) slaughtered his Budn (camels for sacrifice) and got his head shaved."

When `Abdullah bin `Umar set out for Mecca with the intentions performing `Umra in the period of afflictions, he said, "If I should be prevented from reaching the Ka`ba, then I would do the same as we did while in the company of Allah's Messenger (ﷺ) ." So, he assumed the Ihram for `Umra since the Prophet (ﷺ) had assumed the Ihram for `Umra in the year of Al-Hudaibiya. Then `Abdullah bin `Umar thought about it and said, "The conditions for both Hajj and `Umra are similar." He then turned towards his companions and said, "The conditions of both Hajj and `Umra are similar and I make you witnesses that I have made the performance of Hajj obligatory for myself along with `Umra." He then performed one Tawaf (between As-Safa and Al-Marwa) for both of them (i.e. Hajj and (`Umra) and considered that to be sufficient for him and offered a Hadi.