Diagonal Rib. Cast on a number of stitches divisible by six.
Row 1. * Knit four and Purl two. Repeat from * across row. End Purl two.
Row 2. Purl one, * Knit two, Purl four. Repeat from * across row. End Purl three.
Row 3. Knit two, * Purl two, Knit four. Repeat from * across row. End Knit two.
Row 4. Purl three, * Knit two. Purl four. Repeat from * across row. End Purl one.
Continue in this manner, always moving stitch by one every row, to give bias effect. For example, on Knit four and Purl two side of pattern, stitch shifts to right. On Purl four and Knit two side of pattern, stitch shifts to left.
Source: Complete Guide to Modern Knitting and Crocheting