Ikrima bin Khalid reported,
Ikrima asked Ibn Umar 
about performing umrah before hajj, and he replied, "There is no harm in it."Ikrima said, Ibn Umar said, "The Prophet ﷺ performed umrah before he performed hajj."
Azami 5377
Sahihعن عكرمة بن خالد
أنه سأل ابن عمر رضي الله عنهما عن العمرة قبل الحج؟ فقال: لا بأس. قال عكرمة: قال ابن عمر: اعتمر النبي ﷺ قبل أن يحج.
Bukhari narrated it in the chapter on Umrah (1774) from Ahmad bin Muhammad (that is, Marwazi), who said, Abdullah (Ibn Mubarak) informed us, who said, Ibn Jurayj informed us, that Ikrima bin Khalid asked Ibn Umar, and he mentioned it.As for what is reported from Saeed bin Musayab, that a man from the companions of the Prophet ﷺ came to Umar bin Khattab and testified before him that he had heard the Messenger of Allah ﷺ, during the illness in which he died, forbid performing Umrah before Hajj, this contains a break in the chain and an unknown narrator. Abu Dawud narrated it (1793) from Ahmad bin Salih, who said, Abdullah bin Wahb narrated to us, who said, Haywa informed me, who said, Abu Isa Khurasani informed me, from Abdullah bin Qasim, from Saeed bin Musayab, and he mentioned it.This contains three defects. The first is the disagreement over whether Saeed bin Musayab actually heard from Umar bin Khattab, which Imam Ahmad affirmed while Ibn Main denied it. The second is that Abdullah bin Qasim Taymi Basri, though narrated from by a number of transmitters, was not deemed trustworthy by anyone. Ibn Hibban merely mentioned him in "al-Thiqat", which is why Ibn Hajar said of him, "Acceptable," meaning if corroborated, but he was not corroborated, so his hadith is weak. The third is that Abu Isa Khurasani is likewise someone from whom many transmitters narrated, yet no one deemed him trustworthy except Ibn Hibban, which is why the Hafiz said of him, "Acceptable," meaning if corroborated, and if not corroborated, his hadith is weak.For these combined reasons, or for others, Khattabi said in his "Maalim", "There is criticism regarding the chain of this hadith," and he said, "The Messenger of Allah ﷺ performed two Umrahs before his Hajj, and an established, known matter is not to be abandoned for a merely presumed one, and the permissibility of this is a matter of consensus among the scholars, with no disagreement recorded on it." Baghawi followed him in Sharh al-Sunnah (10/7), saying, "There is criticism regarding its chain."