Nafi' narrated from Abdullah bin Umar (may Allah be pleased with them both) that he would mark (ish'ar) the sacrificial camels on the left side of the hump, unless they were unruly and shied away; then, if he was not able to get between them, he would mark them on the right side. When he intended to mark them, he would face the qiblah. When marking them, he would say: 'Bismillah wallahu akbar' (In the name of Allah, and Allah is the Greatest). He would mark them with his own hand and slaughter them (the camels) standing, with his own hand.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10172