Sayyiduna Anas bin Malik (may Allah be pleased with him) said: I heard the Messenger of Allah (peace and blessings be upon him) calling the talbiyah for both together: 'Labbayka 'umratan wa hajjan, labbayka 'umratan wa hajjan' (Here I am for Umrah and Hajj, here I am for Umrah and Hajj).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 8828