What is the ruling on making up missed prayers whose number is unknown, and is it permissible to make them up with the supererogatory prayers?

The view that intentionally omitted prayers must be made up (qada’) is not based on the view that one who abandons prayer is an unbeliever (kafir); there is no necessary connection between the two issues. Some scholars, like the Hanbalis, consider one who abandons prayer to be a kafir and oblige him to make up the prayers, whereas Ibn al-Qayyim and Ibn Hazm hold that there is no obligation to make them up, even though they do not consider him a kafir. There is no harm in following the opinion of those who say that there is no obligation to make up intentionally missed prayers, even if the view is that one who abandons prayer is not a kafir.