Hadith 508500
Chapter 20: Hajj - كتاب الحج
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ نَافِعٍ، أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ، كَانَ إِذَا طَعَنَ فِي سَنَامِ هَدْيِهِ وَهُوَ يُشْعِرُهُ قَالَ بِسْمِ اللَّهِ وَاللَّهُ أَكْبَرُ .
Yahya related to me from Malik from Nafi that Abdullah ibn Umar said, when nicking the hump of his sacrificial animal to brand it, "In the name of Allah, and Allah is greater."
Reference Muwatta Malik 508500
USC-MSA web (English) reference : Book 20, Hadith 147