Ata (may Allah have mercy on him) said that the Messenger of Allah (peace and blessings be upon him) heard a man saying "Labbayk" on behalf of someone, so he said: "If you have performed Hajj yourself, then say the talbiyah on his behalf; otherwise perform Hajj for yourself, then perform it on his behalf."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 8678
Hadith Gradingمحدثین:صحيح لغيره
Hadith Takhrij«صحيح لغيره۔ كتاب الام للشافعي 2/ 157»