Hadith 8:2347
Abu Bakr narrated to us, he said: Abu Bakr ibn Ayyash narrated to us, from Umar ibn Muhammad, from Salim, who said: Ibn Umar entered into ihram for an Umrah, then he traveled for a while, then he said: "The Hajj and the Umrah are nothing but the same. I call you to witness that I have made a Hajj obligatory along with it."
حدثنا أبو بكر قال حدثنا أبو بكر بن عياش عن عمر بن محمد عن سالم قال أحرم بن عمر بعمرة ثم سار ساعة ثم قال ما الحج والعمرة إلا سواء أشهدكم أني قد أوجبت معها حجة