(3) باب النَّحْرِ قَبْلَ الْحَلْقِ فِي الْحَصْرِ
Narrated Al-Miswar:
Allah's Messenger (ﷺ) slaughtered (the Hadi) before he had his head shaved and then he ordered his Companions to do the same.
Reference: Sahih al-Bukhari 1811
In-book reference: Book 27, Hadith 6
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 3, Book 28, Hadith 38