What is the meaning of al-istinjaʾ, washing the knuckles (al-barajim), and al-sabṭ, and what is the difference between sunan and nawāfil and their numbers?

The rulings on istinja’ (purification after defecation/urination) and the finger joints (barajim) have been previously explained. Also, it was clarified that sabt refers to straight, flowing hair without kinks, just as the difference between Sunan (recommended acts) and Nawafil (supererogatory acts), their numbers, and how they are performed, have been addressed in previous fatwas.