Sahih al-Bukhari 1721
Sahih al-Bukhari · Book 25: Hajj (Pilgrimage) · Slaughtering before having one's head shaved
Narrated Ibn `Abbas:
حَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ بْنِ حَوْشَبٍ ، حَدَّثَنَا هُشَيْمٌ ، أَخْبَرَنَا مَنْصُورٌ ، عَنْ عَطَاءٍ ، عَنِ ابْنِ عَبَّاسٍ ـ رضى الله عنهما ـ قَالَ سُئِلَ النَّبِيُّ صلى الله عليه وسلم عَمَّنْ حَلَقَ قَبْلَ أَنْ يَذْبَحَ وَنَحْوِهِ. فَقَالَ " لاَ حَرَجَ، لاَ حَرَجَ ".
The Prophet (ﷺ) 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."