Exothermic reactions release energy in the form of heat, light, sound, etc., to the surroundings while undergoing the chemical reaction processes.
Combustion reactions are also exothermic because they release energy in the form of light and heat and are redox reactions because it absorbs oxygen from the surrounding to undergo the process completely.
Any substance that burns can be considered a combustion reaction as it requires oxygen to continue and releases energy in the form of light and heat.
Hence, combustion reactions are always exothermic in nature.