All other kinds of fasts are Nafl, a term already explained (p. 199).
Nafl are voluntary prayers the performance of which is considered mustahab, or meritorious, but they are not of divine obligation.
He may omit the sunnat and Nafl rak'ats if he chooses; but the three witr rak'ats he must recite at the Salt-ul-'Ish.
A Nafl fast may be broken if the person who intended to keep it receives an invitation to a feast.
In order to relieve him as much as possible, two Nafl rak'ats of a Namz should be said.
According to Bukhr, a woman may not make a Nafl fast without the consent of her husband.
A Namz of some Nafl rak'ats is said and sometimes a Du' is added.
The men then go to the Mosque and after the Namz-i-'Ish they repeat a number of Nafl rak'ats.