Sahih Muslim Book 22, Hadith Number 4841.

Chapter : It is meritorious to sacrifice the animal with one’s own hand and so is meritorious the recitation of Bismillah (in the name of Allah) and Takbir (Allah o-Akbar).

Anas reported that Allah’s Messenger (may peace be upon him) sacrificed with his own hands two horned rams which were white with black markings reciting the name of Allah and glorifying Him (saying Allah-o-Akbar). He placed his foot on their sides (while sacrificing).