The formation of a bond is always exothermic because when two atoms come together to form a bond, their potential energy decreases. Atoms are naturally attracted to each other due to the electrostatic forces between positively charged nuclei and negatively charged electrons. When atoms form a bond, they move to a lower energy state, which is more stable than the separated atoms. The excess energy is released in the form of heat, which makes the process exothermic.
This energy release is what stabilizes the molecule formed by the bond. The stronger the bond formed (for example, a triple bond compared to a single bond), the greater the amount of energy released.