All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
Creed is a form of worship and an act worship cannot be valid (and accepted) except with intention as the Prophet said: "Indeed, actions are judged by intentions. So, a person gets what he had intended."[Al-Bukhari and Muslim]
Intention accompanies the act of worship. So, if you intended that this sheep was for 'Aqeeqah and it fulfilled the conditions for being sufficient -which are the same conditions as the 'Eed sacrifice, (please refer to Fatwa 81799), then is sufficient for you, Allaah willing. The intention of the butcher is unimportant; as he is not the person in charge, he is just like a hired person. This act of worship is peculiar to you and you intended what you wanted from it and you do not need to tell the butcher about your intention from the sheep. But if the butcher slaughtered a sheep and then he sold its meat to you, then this is not sufficient for 'Aqeeqah even if it were a whole sheep as it was slaughtered before your intention for 'Aqeeqah.
For more benefit on 'Aqeeqah, please refer to 81462 and 81526.
Allaah Knows best.