In what programming language did the use of the percent sign (%) to mean modulo/remainder originate?

Question

In what programming language did the use of the percent sign (%) to mean modulo/remainder originate?

This previous post¹ explains that the symbol % was likely chosen because it includes a slash, clever for an operation related to division. It also mentions the influence of C's use of the symbol. However, I'm not certain that it originated in C. The B programming language was a precursor to C, and I've found a User's guide for B (PDF, page 12) that states:

The operator % denotes modulo. If both operands are positive, the result is correct. It is undefined otherwise.

That user's guide is dated 1972 though, approximately when C appeared. That makes it still theoretically possible to have originated in C, but then back-ported to B. I've also not yet been able to find specifications for other languages prior to this indicating use of the % symbol.

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1. To which I believe this question is not a duplicate: That one asks why the modulo operation is fundamental, I'm asking about when the symbol in particular appeared to mean modulo.

Answer 1

The earliest reference I can find is from the "B" programming language developed by Ken Thompson with Dennis Ritchie around 1969. B Reference

As this was an implementation/improvement of BPCL I have to assume the operator was part of BPCL but I cannot find a specific reference for this.