Reference for Shevuot 92:7
וניחוש דלמא בכותל נתחכך תני רבי חייא שעלתה לו נשיכה בגבו ובין אצילי ידיו ודלמא אחר עביד ליה דליכא אחר:
But let us take into consideration that perhaps he rubbed himself against a wall!<span class="x" onmousemove="('comment',' And injured himself; why should he receive compensation from the other without an oath?');"><sup>22</sup></span> - R'Hiyya taught [that the Mishnah deals with a case] where a bite appeared on his back or between his arm-pits.<span class="x" onmousemove="('comment',' Or in the elbow joint, which could not have been caused by rubbing against a wall.');"><sup>23</sup></span> But perhaps someone else did it to him?<span class="x" onmousemove="('comment',' Why should he obtain compensation, without an oath, from the householder? Perhaps another person in the house injured him.');"><sup>24</sup></span> - There was no other.'