It is narrated from Ibn Umar (may Allah be pleased with him) that he said: Performing Umrah before Hajj and offering a sacrifice is more beloved to me than performing Umrah after Hajj in the month of Dhul-Hijjah.
Hadith Referenceمسند الإمام الشافعي / كتاب الحج / 808
Hadith Takhrijاسناده صحيح : اخرجه البيهقي : 4 / 345 ۔ وفى المعرفة السنن والآثار له (2704)۔