What is the combo?
It using the 3.5 D&D rules.
The Infinite Wish Loop!
Per Gate spell you going to have to have be caster level 5 or above to control the efreet
For AD&D 1st Edition the candle is 5,000 gp. However this sequence has a problem. Unlike the 3.5 Gate spell the AD&D gate spell does not place the summoned being under any type of compulsion.
Update I found a combination that would work with AD&D 1st edition that involves two items
As long as you stay within the conditions of the Rod of Beguiling you should be able to gain infinite wishes.
I emailed Eliezer Yudkowsky, the author of HPMOR -- this was his response:
So I think that's going to be as good as we can get. Now let us give thanks to Eliezer for taking the time to respond to such a question! :)