What are the sixteen prayers that scholars have mentioned are not intended for their own sake, and what is the voluntary fasting not intended for its own sake?

The jurists mentioned non-intended prayers that can overlap, such as تحية المسجد (greeting the mosque prayer), الاستخارة (prayer for guidance), and سنة الوضوء (the prayer after ablution). As for non-intended voluntary fasting, it is the absolute supererogatory fast. Supererogatory fasting is divided into Sunnah (recommended) and absolute. As for the days of fasting that are Sunnah, if one intends to fast a non-Sunnah fast on them, it is permissible, because the aim is to achieve any fasting on those days.