Fiqh-us-Sunnah Volume 5, Hajj and ‘Umrah, Fiqh 5.034.

Ifrad means a pilgrim intending to perform Hajj only should, while at the miqat, make intention for Hajj only. While making talbiyah he or she should say, Labbaik bihajj “(O Allah, I answer your call to perform Hajj),” and must keep his or her Hajj garb until all the rites of Hajj are completed. Then, if such a pilgrim desires, he or she may perform an ‘Umrah.