Abu Isrāʾīl; he vowed to stand in the sun, never sit down, never seek shade, and to fast.” The Prophet ﷺ said, “Tell him to sit down, to seek shade, to speak, and to complete his fast.”

Ruling on a vow that involves sin
194 – Since this man’s vow combined an act that is sunnah with another that is an innovation, the Prophet ﷺ ordered him to fulfill the sunnah part and abandon the innovative part, just as al-Bukhārī¹ relates from ʿĀʾishah — may Allah be pleased with her — that the Prophet ﷺ said, “Whoever vows to obey Allah, let him obey Him; and whoever vows to disobey Him, let him not disobey Him.”

195 – The leading scholars of the religion are unanimously agreed on this principle, yet they differed over whether such a vow requires the expiation of an oath or is simply a non-legislated vow that incurs nothing, after first agreeing that the act itself must not be carried out. Some said that nothing is due, and this is the position of Abū Ḥanīfah, al-Shāfiʿī, and others, because neither this ḥadīth nor any other shows that the Prophet ﷺ ordered expiation. Others held that the expiation of an oath is required; this is the apparent view of Aḥmad².

196 – Their evidence is the report in Ṣaḥīḥ Muslim³ in which the Prophet ﷺ said, “The expiation for a vow is the expiation for an oath.”