He—peace and blessings be upon him—said to her, “Were you making up any missed fasts?”
She answered, “No.”
He replied, “Then it does you no harm, since it was only a voluntary fast.”

Al-Shāfiʿī supported this view with the ḥadīth of ʿĀʾishah, who related:

“The Messenger of Allah—peace and blessings be upon him—entered my house and I said, ‘I have put something aside for you.’ He said, ‘I had intended to fast today, but bring it here.’”

The report attributed to ʿĀʾishah and Ḥafṣah, however, is not connected (its chain of transmission is mursal).

There is another reason for their divergence on this question: whether a voluntary fast should be analogized to voluntary prayer or to a voluntary ḥajj. They unanimously agree that whoever begins a voluntary ḥajj or ʿumrah and then abandons it must perform it later in compensation, and they likewise agree—so far as I know—that whoever leaves a voluntary prayer unfinished is not required to make it up. Those who liken fasting to prayer contend that it more closely resembles prayer than ḥajj, for ḥajj has a special ruling in this respect, namely that one who invalidates it must continue with its rites to the end.

If a person breaks a voluntary fast through forgetfulness, the majority hold that no makeup is required, whereas Ibn ʿUlayyah maintained that a makeup is obligatory by analogy with ḥajj. It is possible that Mālik understood the ḥadīth of Umm Hānī in light of forgetfulness.

The ḥadīth of Umm Hānī was recorded by Abū Dāwūd, who also transmitted the ḥadīth of ʿĀʾishah in wording close to what we have cited, as well as the very report of ʿĀʾishah and Ḥafṣah itself.