Mon Tricot 1500 Patterns, p.86.
Note: the book instructions say “knit into front and back of next stitch alternately 3 times” instead of (p1, k1, p1) in next stitch. However, while that instruction is clearly meant to make three stitches, it doesn’t match the picture. I think it could be (purl in front loop, purl in back loop, purl in front loop), though.
Shown with a cast-on count of 21 stitches.