Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said: That I perform Umrah before Hajj and take a sacrificial animal (hady) is dearer to me than performing Umrah after Hajj in Dhu al-Hijjah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 8737