Anas said that God’s Messenger sacrificed with his own hand two horned rams which were white with black markings, mentioned God’s name and said, "God is most great.” He added:

I saw him placing his foot on their sides and saying, "In the name of God. God is most great.” (Bukhari and Muslim.)

عَن أنس قَالَ: ضَحَّى رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ بِكَبْشَيْنِ أَمْلَحَيْنِ أَقْرَنَيْنِ ذَبَحَهُمَا بِيَدِهِ وَسَمَّى وَكبر قَالَ: رَأَيْته وضاعا قَدَمَهُ عَلَى صِفَاحِهِمَا وَيَقُولُ: «بِسْمِ اللَّهِ وَاللَّهُ أكبر»