In Mandarin phonology, a syllable's rime consists of its vowel (and any ending consonant), while the lexical tone is treated as a suprasegmental feature; consequently, syllables sharing identical vowels and differing only in tone are considered to have matching rimes and thus rhyme.
The claim concerns a definitional matter in Mandarin phonology regarding the constituents of a rhyme (the rime component versus the lexical tone). Because this is a standard linguistic classification based on direct definitions of Mandarin syllable structure rather than a contested empirical hypothesis, it represents common knowledge for which no empirical paper citation is required.