I saw Abu Hurayrah performing ablution on top of the mosque, so I asked him, "What are you performing ablution from?"He replied, "From pieces of dried curd I ate. I heard the Messenger of Allah ﷺ say, 'Perform ablution from whatever has been touched by fire.'"
حدثنا وكيع قال حدثنا عبد العزيز يعني ابن عبد الله بن أبي سلمة عن ابن شهاب عن عمر بن عبد العزيز
رأيت أبا هريرة يتوضأ فوق المسجد فقلت مم تتوضأ قال من أثوار أقط أكلتها سمعت رسول الله ﷺ يقول توضئوا مما مست النار
Its isnad is sahih, previously mentioned at 7594, 2/457-458, and 469-470 of the printed edition. Al-Athwar is the plural of thawr (with a "th" sound), meaning a piece, and al-aqit is dried milk that is cooked and eaten afterward.