Q. If one makes an intention to keep a Nafl fast at night and misses Sehri, can one choose not to fast after Sehri?
A. If an intention to keep a Sunnah or Nafl fast is made at night, one cannot choose not to fast after Subah Saadiq/Sehri has terminated. The fast must be kept and observed for the day. If the fast is broken, a Qadha of the fast must be kept.
However, if after making the intention to keep a Sunnah or Nafl fast at night, one chooses not to fast before Subah Saadiq/Sehri is terminated, one does not have to keep and observe the fast for the day. (Al-Ikhtiyaar-Li-Taleelil-Mukhtaar 1/135)
Allah Ta’ala Knows Best
Mufti Ismaeel Bassa