You wil need:
1 bar laundry soap like Fels Naptha or Zote, or Ivory - Zote can be found in hispanic grocery stores
1 Box Borax - found in the laundry aisle
1 box Washing Soda or Oxi Clean, orBaking soda - (Washing Soda AKA soda ash AKA sodium carbonate available in some grocery stores made by Arm and Hammer or you may find it art supply stores in the dyeing section)
OPTIONAL- essential oil of your choice, I didnt do it but I think tea tree might be nice.
Some recipe considerations, there are many variations to be found online but I based mine on this here http://www.thegreenguide.org/article/diy/household
Powdered Laundry Detergent
# 1 Cup Grated Fels Naptha Soap
# 1/2 Cup Washing Soda
# 1/2 Cup Borax
# For light load, use 1 Tablespoon. For heavy or heavily soiled load, use 2 Tablespoons.
I adjusted for the fact that Zote is at least twice as big as a Fels Naptha bar, and personally if I'm going to make a mess I'd rather double or triple the recipe which still easily fit in the food processor, also I used baking soda AND oxi-clean instead of the washing soda, the reason being that I could not find the washing soda, and Oxi-clean is essentially the same thing but with added peroxide* which does add a mild bleaching action, should be "color safe" though. It is also my understanding that baking soda is similar to washing soda but half as alkaline, so using baking soda will give you a gentler blend.
*note don't try and make the liquid recipe behind the link with "oxi clean" because the peroxide will make the whole mess foam, that was what I originally tried -- and ended up with useless semi solid foamy spooge.