Why do we say "There is no might nor power except with Allah" upon hearing the muezzin say "Hasten to prayer, hasten to salvation," and what do we say upon hearing "Prayer is better than sleep"?

The listener says, when the muezzin says: "Haya ala as-Salah (Hasten to the prayer), Haya ala al-Falah (Hasten to salvation)": "La hawla wa la quwwata illa billah (There is no might nor power except with Allah)," as was established from the Prophet, peace and blessings be upon him, and his companions. This was an exception to the general saying: "When you hear the muezzin, say as he says." The listener is compensated for missing the reward of repeating the hayalah (Hasten to prayer/salvation) with the reward of the hawqalah (There is no might nor power except with Allah), because the purpose of the hayalah is an invitation to prayer, and that is achieved by the muezzin. And "La hawla wa la quwwata illa billah" means that this is a great matter that the servant cannot accomplish except with Allah's grace and help.