Abu Huraira reported that the rat (is the result of) metamorphosis (of a group of Bani Isra'il) and the proof of this is that when the milk of goat is placed before it, it drinks it, and when the milk of the camel is placed before it, it would not taste it at all. Ka'b said: Did you hear it from Allah's Messenger (ﷺ)? Thereupon he said: Has Torah been revealed to me?
Source: sunnah.com
Other translations
Arabic
وَحَدَّثَنِي أَبُو كُرَيْبٍ، مُحَمَّدُ بْنُ الْعَلاَءِ حَدَّثَنَا أَبُو أُسَامَةَ، عَنْ هِشَامٍ، عَنْ مُحَمَّدٍ، عَنْ أَبِي هُرَيْرَةَ، قَالَ " الْفَأْرَةُ مَسْخٌ وَآيَةُ ذَلِكَ أَنَّهُ يُوضَعُ بَيْنَ يَدَيْهَا لَبَنُ الْغَنَمِ فَتَشْرَبُهُ وَيُوضَعُ بَيْنَ يَدَيْهَا لَبَنُ الإِبِلِ فَلاَ تَذُوقُهُ " . فَقَالَ لَهُ كَعْبٌ أَسَمِعْتَ هَذَا مِنْ رَسُولِ اللَّهِ صلى الله عليه وسلم قَالَ أَفَأُنْزِلَتْ عَلَىَّ التَّوْرَاةُ
sunnah.com