Shulchan Arukh Yoreh De'ah · Siman 7

English

Seif 1 A person may set a knife on a wheel of stone or wood that rotates by one's hand or foot, and proceed (with the contraption) to the neck of the animal or fowl until it is slaughtered by turning the wheel. (and it is acceptable). And if water rotates the wheel and he places the neck of [the animal] opposite it while it was turning causing it to be slaughtered, it is unacceptable.An exemption is made if a person caused the water to flow until they turned the wheel and caused it to slaughter by turning it, [if so the slaughter] is acceptable after the fact because the act came as a result of man's actions. However (a slaughtering that results) from a second rotation is unacceptable because the force did not come from man's power, but from the power of the flowing water.