Al-Haythami said in Majmaʿ al-Zawaʾid (1/236):

“Al-Tabarani narrated it in al-Awsat, and recorded it in al-Kabir as a report attributed to the Companion Ibn Masʿud; and its chain of transmission is good.”

I say: The chain of transmission in al-Kabir is authentic, for al-Tabarani recorded it (9/282/1921 and 1922) by way of al-Thawri and Zaʾidah, from Abu Miskin, with this wording attributed to the Companion. Yet it has the ruling of a report attributed to the Prophet in meaning, so it does not impair the report attributed to the Prophet, as is apparent.

I then found that what has preceded from al-Haythami was cited by al-Mundhiri in al-Targhib (1/103/4). I even thought that he had merely followed him, except that he added:

“In one version which he narrated in al-Kabir as a report attributed to the Companion, he said: ‘Clean between the five fingers, lest Allah fill them with Fire.’”

I say: Al-Tabarani recorded it (9213) by way of Talhah ibn Musarrif, who said: “I was told on the authority of Abdullah ibn Masʿud that he said: ...”—and he then cited it.

Its narrators are trustworthy, apart from the unnamed man. Al-Mundhiri then said:

“His words, ‘You will surely go to great lengths in washing them,’ mean: you will surely be thorough in washing them; or the Fire will surely be thorough in burning them. Nahk means going to extremes in everything.”

The explanation of nahk as stated is well known, but it does not accord with the wording he reported in the hadith. For this reason, al-Hafiz al-Naji critiqued him in his ʿUjalah (p. 42), saying:

“His wording, ‘la-tantahikanna (“you will surely violate”) the fingers through purification, or la-tantahikannahā (“the Fire will surely violate them”),’ and his explanation of it—as a form with an added taʾ and a kasrah on the haʾ, derived from intihak (violation)—is certainly not what is intended here.”