Sahih Muslim Book 7, Hadith Number 3000.

Chapter : Regarding one who shaves before offering the sacrifice or offers sacrifice before throwing (the stones at Jamra).

Abdullah b. ‘Amr (b. al-‘As) (Allah be pleased with him) reported that a person came to Allah’s Apostle (may peace be upon him) and said: I got (my head) shaved before sacrificing the ,animal, whereupon be (the Holy Prophet) said: Sacrifice the animal (now); there is no harm in it. He (the person said): I sacrificed the animal before throwing pebbles, whereupon he said: Throw pebbles (now); there is no harm in it.