Sahih Al Bukhari Hadith Number 1721

Narrated Ibn `Abbas: The Prophet (peace be upon him) was asked about a person who had his head shaved before slaughtering (his Hadi) (or other similar ceremonies of Hajj). He replied, “There is no harm, there is no harm.”

25  Hajj (Pilgrimage)
Hadith number 1721
Volume no 2
Chapter: 125 (Slaughtering before having one’s head shaved)