Musnad Ahmad 28:554

Ya'qub narrated to us, my father narrated to me, from Salih. Ibn Shihab said: Isa ibn Talhah ibn Ubayd Allah narrated to me that he heard Abdullah ibn Amr ibn al-As saying: The Messenger of Allah (peace and blessings of Allah be upon him) stood on the Day of Sacrifice (Yawm al-Nahr) upon his riding beast, and they began to ask him. One of them would say: "O Messenger of Allah, I did not realize that the stoning (of the Jamarat) was before the sacrifice, so I sacrificed before I stoned." The Messenger of Allah (peace and blessings of Allah be upon him) said: "Stone, and there is no harm." Another began to say: "O Messenger of Allah, I did not realize that the sacrifice was before the shaving (of the head), so I shaved before I sacrificed." The Messenger of Allah (peace and blessings of Allah be upon him) would say: "Sacrifice, and there is no harm." He said: I did not hear him asked on that day about any matter that a person might forget or be ignorant of, regarding performing some actions before others, or similar things, but that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Do it, and there is no harm."