Ibn Ṭalḥah ibn Yazīd ibn Rakānah related—from ʿUbaydullāh al-Khawlānī—from Ibn ʿAbbās, who said: “ʿAlī entered my house and asked for water to perform ablution. We brought a wooden bowl that held about one mudd, or a little less, set it before him, and he had just relieved himself. He then said, ‘O Ibn ʿAbbās …’ ”—and so forth.

This chain of transmission is sound.

Thus, this ḥadith is virtually explicit in supporting Shaykh al-Islām’s view that one may sprinkle water on the foot while it is still inside the sandal. Yet that does not nullify the other Sunnah—wiping over the sandals, just as over leather socks and cloth socks—by reinterpreting “wiping” to mean “sprinkling,” as the Shaykh proposed, for there is no decisive indicator that would shift the wording from its literal sense to a figurative one. Allah knows best.

Later I found a clear statement by Shaykh al-Islām permitting the wiping over sandals on condition that removing them would entail hardship. He wrote in al-Fatāwā (2/85): “It is reported that the Prophet ﷺ wiped over his feet when the need arose, such as when he wore sandals that were difficult to take off.” In al-Ikhtiyārāt he further qualified this: “unless one can remove them with the hand or the other foot.”

10 – Nullifiers of ablution
1, 2 – Urine and feces: “Allah does not accept the prayer of any one of you when he has experienced a state of hadath until he performs ablution” (agreed upon); and “No ablution is required save for a sound or an odor” (Tirmidhī: sound; Ibn Mājah; Bayhaqī; Aḥmad 2/410).
3 – Pre-seminal fluid (madhy): it necessitates ablution (agreed upon).