“But whether the person being baptized should be wholly immersed, and whether thrice or once, whether he should only be sprinkled with poured water – these details are of no importance, but ought to be optional to churches according to the diversity of countries. Yet the word ‘baptize’ means to immerse, and it is clear that the rite of immersion was observed in the ancient church.”
John Calvin, Institutes of Christian Religion, Book IV, Ch. 15, Sec. 19 (p. 1320).