When is it said about a supererogatory prayer that it is not to be made up for, and is that because it is a Sunnah whose time has passed, even though the Prophet, may God’s prayers and peace be upon him, used to make up for some supererogatory prayers, such as Witr?

If the reason for a restricted supererogatory prayer (nafl) passes, it is not made up (qada’). For example, the eclipse prayer, if one learns of it after it has ended, or the greeting of the mosque (tahiyyat al-masjid), if one sits for a long time before remembering to perform ablution. The rule is that any supererogatory prayer restricted by a reason is not made up if its reason has passed. However, the Prophet, peace and blessings be upon him, used to make up his Witr prayer during the day as twelve rak’ahs, because he used to pray eleven rak’ahs for Witr, so he would make it even (shaf’a) since the time for Witr had passed.