Charles Spurgeon Commentary Numbers 19:2-3

"This is the statute of the law which Jehovah hath commanded, saying, Speak unto the children of Israel, that they bring thee a red heifer without spot, wherein is no blemish, [and] upon which never came yoke. And ye shall give her unto Eleazar the priest, and he shall bring her forth without the camp, and one shall slay her before his face:" — Numbers 19:2-3 (ASV)

This was not a usual sacrifice, for the beasts offered were as a rule males; but this was to be a special sacrifice. It was not to be killed by the priest, as other sacrificial offerings were; but the Lord said, "One shall slay her before his face."