It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) was asked about putting the slaughtering of the sacrificial animal and the shaving of the head before or after one another, and he (peace and blessings be upon him) said: "There is no harm."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10863