From Sahih Bukhari (Hadith 1774):
Narrated Ibn Juraij:`Ikrima bin Khalid asked Ibn `Umar about performing `Umra before Hajj. Ibn `Umar replied, "There is no harm in it." `Ikrima said, "Ibn `Umar also said, 'The Prophet (ﷺ) had performed `Umra before performing Hajj.'" Narrated `Ikrima bin Khalid: "I asked Ibn `Umar the same (as above)
Reference: Bukhari 1774