If the butcher makes it a condition that he receives a wage for slaughtering or if this is the `Urf (custom), it is Wajib (obligatory) on you to pay this to him but not in the form of some of the meat from the Ud-hiyah. Otherwise, it is not obligatory on you to pay him a wage even though it is a good deed if you do it voluntarily. This is because the Prophet (peace be upon him) said:
...Requite him who does a favor to you...
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.