Read these:

http://physicsworld.com/cws/article/print/24493

http://www.livescience.com/mysteries/080926-llm-ice-cubes.html

http://blogs.chron.com/sciguy/archives/2006/06/does_hot_water.html

There are literally hundreds of sites to go through.

You may also like this one:

http://www.scientificamerican.com/article.cfm?id=is-it-true-that-hot-water

This is a perennial question. Why not ask your colleague to actually do the experiment?

I performed this experiment in a laboratory with all the proper equipment, and could never make hot water freeze faster than cold water.

It does not.

Thanks for the replys guys,

I suppose there is only one thing for it. As TVP45 says, he'll have have to the experiment to find out.

Its funny, it seems like such an intuitive thing, cold water will freeze faster, yet I can recall all through high school it was a general assumption that hot water froze faster than cold, I can even recall one of my high school science teachers explaining that water expands when it freezes and hot water is expanded more than cold already so its closer to the state of being frozen. To a 14 year old this made sense, imagine my surprise when the conversation arose in freshman physics and I discovered it wasn't proven or even accepted by most scientists that hot water freezes faster. Yet every night my wife fills our ice cube trays with hot water (we get our new fridge with an ice maker in 2 weeks ) Go figure.

There are some reasons to use hot water in your ice cube trays. If they're aluminum and the fridge is not very frost free, the hot water melts a good contact surface for the bottom of the tray. If the water was previously boiled, it has less gas in it and thus will make clearer cubes.

Last year during winter, -30 below temp was perfect for the fast freeze test. I took a glass of cold water and hot water, through it up in the air and the cold water hit the ground. The hot water vaporized and froozen pellets hit the ground.

Gotta run!