[The Ruling on One Who Vows a Thousand Pilgrimages]

Answer – and Allah is the One who grants success: This vow is invalid, because it does not fall under the scope of what is within one’s capability. In such a case, what is required is the expiation for an oath; and this is the position of the madhhab, as in al-Sharḥ.
If it is said: Why do you not say that this vow-maker should perform ḥajj as much as he is able, and then offer the expiation for an oath for what remains?
We say: It is stated in al-Sharḥ, quoting some of the scholars of the madhhab, that no scholar has ever adopted this opinion. If that is the case, then it is not permissible to adopt it, because it contradicts consensus.
The proof for this issue is His saying the Exalted: “Allah does not burden a soul beyond its capacity.” [al-Baqarah:286] and the like.

Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2