What is the ruling on combining two prayers (Dhuhr and Asr) for a non-traveler due to forgetfulness, and is it a condition that fifteen days or a specific period pass before combining again, and has anything been reported regarding this from the Prophet, peace and blessings be upon him, or in the narrations?

Whoever forgets a prayer must pray it immediately upon remembering it, for the Prophet, peace and blessings be upon him, said: "Whoever forgets a prayer or sleeps through it, its expiation is to pray it when he remembers it." This is not considered combining prayers, nor should one wait for the time of another prayer to pray it with it. There is no specific duration limit for this. As for permissible combining of prayers, it has its reasons (travel, rain, fear, illness) and is not tied to a specific duration.