A voluntary (nāfila) fast is one that is observed outside the month of Ramadan on a non-obligatory basis, meaning that it is neither obligatory (farḍ) nor mandatory (wājib) upon the individual. Nevertheless, even though it is voluntary, once an act of worship has been commenced, it must be completed. Accordingly, as with other voluntary acts of worship, according to the Ḥanafī school, it is wājib to make up a voluntary fast that has been broken.
The Qur’anic verse, “Do not invalidate your deeds” (Muḥammad 47:33), is cited as evidence for this ruling.
In addition, in a hadith reported in Abū Dāwūd, our mother ʿĀʾisha (may Allah be pleased with her) relates that while she and Ḥafṣa were fasting, a gift was brought to them. As they desired it, they ate from it. When they later asked the Messenger of Allah (peace and blessings be upon him) about this, he replied:
“There is no sin upon you because of this, but observe a fast on another day.”
(Abū Dāwūd, Ṣiyām, 73; al-Tirmidhī, Ṣawm, 36)