עגלה ערופה דברים כ"א,1-9

If one be found slain in the land which the LORD thy God giveth thee to possess it, lying in the field, and it be not known who hath smitten him; then thy elders and thy judges shall come forth, and they shall measure unto the cities which are round about him that is slain. And it shall be, that the city which is nearest unto the slain man, even the elders of that city shall take a heifer of the herd, which hath not been wrought with, and which hath not drawn in the yoke. And the elders of that city shall bring down the heifer unto a rough valley, which may neither be plowed nor sown, and shall break the heifer’s neck there in the valley. And the priests the sons of Levi shall come near—for them the LORD thy God hath chosen to minister unto Him, and to bless in the name of the LORD; and according to their word shall every controversy and every stroke be. And all the elders of that city, who are nearest unto the slain man, shall wash their hands over the heifer whose neck was broken in the valley. And they shall speak and say: ‘Our hands have not shed this blood, neither have our eyes seen it. Forgive, O LORD, Thy people Israel, whom Thou hast redeemed, and suffer not innocent blood to remain in the midst of Thy people Israel.’ And the blood shall be forgiven them. So shalt thou put away the innocent blood from the midst of thee, when thou shalt do that which is right in the eyes of the LORD.

וערפו AND THEY SHALL STRIKE OFF [THE HEIFER’S] NECK — i.e. one breaks its neck with a hatchet. The Holy One, blessed be He, says, as it were, Let a heifer which is only one year old and which therefore has brought forth no fruits (no offspring) have its neck broken at a spot (the untilled valley) which has not brought forth fruits, to expiate for the murder of him whom they did not permit further to beget children (Sotah 46a).

And the man knew Eve his wife; and she conceived and bore Cain, and said: ‘I have agotten a man with the help of the LORD.’ And again she bore his brother Abel. And Abel was a keeper of sheep, but Cain was a tiller of the ground. And in process of time it came to pass, that Cain brought of the fruit of the ground an offering unto the LORD. And Abel, he also brought of the firstlings of his flock and of the fat thereof. And the LORD had respect unto Abel and to his offering; but unto Cain and to his offering He had not respect. And Cain was very wroth, and his countenance fell. And the LORD said unto Cain: ‘Why art thou wroth? and why is thy countenance fallen? If thou doest well, shall it not be lifted up? and if thou doest not well, sin coucheth at the door; and unto thee is its desire, but thou mayest rule over it.’ And Cain spoke unto Abel his brother. And it came to pass, when they were in the field, that Cain rose up against Abel his brother, and slew him. And the LORD said unto Cain: ‘Where is Abel thy brother?’ And he said: ‘I know not; am I my brother’s keeper?’ And He said: ‘What hast thou done? the voice of thy brother’s blood crieth unto Me from the ground. And now cursed art thou from the ground, which hath opened her mouth to receive thy brother’s blood from thy hand. When thou tillest the ground, it shall not henceforth yield unto thee her strength; a fugitive and a wanderer shalt thou be in the earth.’ And Cain said unto the LORD: ‘My punishment is greater than I can bear. Behold, Thou hast driven me out this day from the face of the land; and from Thy face shall I be hid; and I shall be a fugitive and a wanderer in the earth; and it will come to pass, that whosoever findeth me will slay me.’ And the LORD said unto him: ‘Therefore whosoever slayeth Cain, vengeance shall be taken on him sevenfold.’ And the LORD set a sign for Cain, lest any finding him should smite him. And Cain went out from the presence of the LORD, and dwelt in the land of Nod, on the east of Eden.