Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) used to say that Sayyiduna Umar (may Allah be pleased with him) used to say: If you separate Hajj and Umrah, and perform Umrah outside the months of Hajj, this makes your Hajj and your Umrah more complete.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 8817