5 – Shaykh Muḥammad ibn ʿAbd al-Wahhāb said: Sin can have an effect on the land, and so can obedience. Therefore, setting aside a particular spot for fulfilling a vow is unobjectionable provided that no prohibitive factor exists. A prohibition is present if the place was ever the site of one of their festivals—even after the festival has long ceased—or if it once contained an idol from the Age of Ignorance, even after the idol itself has disappeared. Whenever any of that applies, it is impermissible to carry out what was vowed in that spot, because such a vow constitutes disobedience.

6 – The same Shaykh Muḥammad also said: The hadith cautions against resembling the polytheists in their festivals, even when one does not intend such resemblance. Shaykh ʿAbd al-Raḥmān ibn Ḥasan added: The report forbids making the remnants of the idol-worshippers a site of devotion, for they have become places of what Allah has forbidden—polytheism and sins. Although the narration is framed around a vow, its ruling embraces every act of worship; none of them may be performed in those defiled places.

7 – On the Prophet’s statement, “Fulfil your vow,” Shaykh al-Islām said: This indicates that slaughtering an animal in a place where their festival is held, or where their idols stand, is disobedience to Allah for several reasons:
First: The command “Fulfil your vow,” joined to its cause by the particle faʾ (“then”), links the ruling to the description, showing that the description is the cause of the ruling. Hence the command to fulfil applies only when the act is not sinful; had it not been sinful, fulfilling it would have been permissible.
Second: Immediately afterwards he said, “There is no fulfilment of a vow that involves disobedience to Allah.” If the case under discussion were not included in that general wording, there would be no connection between the two statements. When the Prophet, peace and blessings be upon him, was asked about the two situations, he told him, “Fulfil your vow”—that is, as long as nothing renders slaughter there unlawful—and he forbade it when such a factor is present.
Third: Had slaughtering at the site of their festival been permissible, the Prophet would have allowed the person who made the vow to honour it, just as he permitted the woman who vowed to beat the tambourine to do so; indeed, he would have required him to fulfil it.