Ikrimah bin Khalid asked Ibn Umar (may Allah be pleased with them both) about performing Umrah before Hajj, and he said: There is no harm for anyone if he performs Umrah before Hajj. Ikrimah said: Ibn Umar said: The Prophet (peace and blessings be upon him) performed Umrah before he performed Hajj.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 8784