Musnad Ahmad 28:8

Muhammad ibn Ja‘far narrated to us, Ma‘mar informed us, Ibn Shihab narrated to us, from ‘Isa ibn Talhah, from ‘Abdullah ibn ‘Amr ibn al-‘As, who said: I saw the Messenger of Allah (peace and blessings of Allah be upon him) standing on his riding camel at Mina. A man came to him and said: "O Messenger of Allah, I was of the opinion that the shaving (of the head) was before the slaughtering, so I shaved before I slaughtered." He said: "Slaughter, and there is no harm." Then another came to him and said: "O Messenger of Allah, I was of the opinion that the slaughtering was before the stoning, so I slaughtered before I stoned." He said: "Stone, and there is no harm." He said: He was not asked about anything that a man had done before another (in sequence) except that he said: "Do it, and there is no harm."