Abdullah bin Sharik al-Amiri said: I asked Sayyiduna Ibn Umar, Sayyiduna Ibn Abbas and Sayyiduna Ibn al-Zubayr (may Allah be pleased with them) about performing Umrah before Hajj, and they said: "It is the Sunnah of the Messenger of Allah (peace and blessings be upon him): one first arrives and performs Tawaf of the House and the Sa'i between Safa and Marwah, then comes out of (ihram), even if that is only one day before Arafah, then enters ihram for Hajj; in this way he will have combined both Umrah and Hajj."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13891