From Sahih Muslim (Hadith 3161):
Adullah b. 'Amr (b. al-'As) (Allah be pleased with him) reported that a person came to Allah's Apostle (ﷺ) 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 sacripced the animal before throwingpebbles. whereupon he said: Throw pebbles (now) ; there is no harm in it
Reference: Muslim 3161