in the Sahīh, in which he said:

“The expiation for a vow is the expiation for an oath.”

He also said, “A vow is an oath.” And it is reported from him in the Sunan:

“A vow involving disobedience is not binding, and its expiation is the expiation for an oath.”

We have already mentioned the occasion of the verse’s revelation. A similar example is what al-Bukhārī narrated in his Sahīh from Ibn ‘Abbās:

“The Prophet, may Allah bless him and grant him peace, saw a man standing in the sun and asked, ‘What is this?’ They replied, ‘This is Abū Isrā’īl. He has vowed to remain standing, not to seek shade or speak, and to fast.’ He said, ‘Tell him to speak, seek shade, sit down, and complete his fast.’”

Since he had vowed to perform acts of worship that were not prescribed—remaining silent, standing, and exposing himself to the sun—the Prophet commanded him to do what was prescribed, namely fasting in his case, and forbade him to do what was not prescribed.

But if someone is unable to perform what he has vowed, or doing so entails hardship, he should offer expiation and perform a substitute for what he vowed. This is illustrated by the hadith of ‘Uqbah ibn ‘Āmir, whose sister vowed to perform Hajj on foot. The Prophet, may Allah bless him and grant him peace, said:

“Allah has no need for your sister to torment herself. Tell her to ride and offer a sacrificial animal”—another narration reads, “and fast.”

Thus, this man who pledged to Allah Most High to fast half the time, when doing so has harmed his mind and body, must refrain from fasting, take what will restore his mental and physical health, and offer the expiation for an oath. He should refrain from fasting for as long as is needed to restore his mental and physical health