It is narrated from Nafi' (may Allah have mercy on him) that Abdullah bin Umar (may Allah be pleased with them both) intended to perform Hajj in the year of turmoil, put on the Ihram, then reflected and said: Hajj and Umrah are both the same; I make you witnesses that I have made Umrah obligatory along with Hajj.
Hadith Referenceمسند الإمام الشافعي / كتاب الحج / 810
Hadith Takhrijاخرجه البخاري، الحج، باب طواف القارن (1639) ، (1640) ومسلم، الحج، باب جاز التحلل بالإحصار وجواز القرآن..... الخ (1230)۔