It says in Brachos 5B that R' Yochanan used to show people his tenth son's bone (all of his children passed away, and he used to carry a bone of his tenth child).
How was he allowed to not bury this bone?
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See the Q&A cited in yydl's answer to a related question:
Rashi to Berachos there says that it was a piece less than the size of a barleycorn, which isn't subject to tum'ah and therefore doesn't require burial. Aruch, and Rashbam to Bava Basra 116a (both cited in Mesores Hashas to Berachos there) explain that it was a tooth, which according to many posekim doesn't require burial either.
Aside from this, some other commentaries (cited in the back of the Nehardea edition of Berachos) explain the phrase differently, as "a bone from the bereavement meal (סעודת הבראה)." According to this approach, it wasn't a human bone at all.