HCl (hydrochloric acid) and NH3 (ammonia) do not undergo combustion.

Combustion is a chemical process that involves a rapid reaction between a substance with an oxidant, usually oxygen, to produce heat and light.

While HCl and NH3 can react to form ammonium chloride (NH4Cl), this reaction is not considered combustion. It is an acid-base reaction, not a combustion reaction.

Here is the chemical equation for the reaction between HCl and NH3:

HCl(g) + NH3(g) → NH4Cl(s)