NAFAL CATEGORY OF FASTING

All classes of Nafl Saum are valid with a niyyat made prior to Nisfun-Nahar. It is preferable to make the Niyyat at night; however, as said, it will be valid even if not made at night.
(1)The sunnat fasts also fall in the Nafl category.
(2) Thus, for Saum belonging to the first category of Wajib and for Nafl Saum, a niyyat made prior to Nisfun-Nahar will suffice.
(3) Once a Nafl Saum has been commenced, it to Incumbent to complete It.

(4) It is not permissible to nullify a Nafl fast without valid reason.
(5) If a Nafl fast is broken, it is obligatory to make Qadha of it.
(6) A Mutlaq (i.e. without any descriptive condition) niyyat suffices for the validity of Nafl Saum. Thus, the Niyyat: 'I shall be fasting,' suffices.
(7) A riiyyat made for Nafl Saum during the night may be cancelled before Subah Sadiq, and qadha for the intended Nafl Saum will not be obligatory.
(8) A niyyat made for Nafl Saum after Subah Sadiq, but before Nisfun-Nahar, makes the fast incumbent. If the fast is broken, qadha becomes obligatory.
(9) It is permissible to end a Nafl Saum to honor one's guests by participating in meals with them. The Saum thus broken should be made qadha.
(10) When the husband is present, it is not permissible for the wife to engage in Nafl Saum without his consent. If she kept a Nafl Saum without his consent, it will be permissible for her to break it if he instructs her to do so. She has to make qadha of the fast whenever her husband gives her the permission to do so.
(11) The incidence of haidh (menses) during a Nafl fast will necessitate qadha. If during the day when a woman is keeping a Nafl fast she menstruates, the Saum will be broken. Qadha of the day is necessary.
(12) A Qadha fast was commenced. However, niyyat for the Qadha was not made during the night as is required by the Shariah. The niyyat was made only after Subah Sadiq. The qadha is not valid. However, this fast will be a Nafl one. The fast should not be broken. If it is broken qadha will have to be made.