There are many different variations of what is called the Quaker rib, which may be worked on any number of stitches. The simplest involve three or four rows of stockinette followed by three or four rows of reverse stockinette.
This pattern is slightly more complicated, with one row of purls thrown into a field of knit rows, followed later by a wider stripe of reverse stockinette.
Rows 1, 3, 5 and 6: Knit.
Rows 2 and 4: Purl.
Rows 7, 9 and 11: Knit.
Rows 8 and 10: Purl.
Rows 12 and 14: Knit.
Row 13: Purl
Repeat these 14 rows for pattern.