Responsa for Eruvin 81:7

בדורו של רבן גמליאל עבוד כר"ג בדורו של רבי יוסי עבוד כרבי יוסי

Said R'Meir: Although R'Gamaliel laid down that 'there is no need to interrupt it', he agrees nevertheless that [the fasts on these days] must not be concluded,<span class="x" onmousemove="('comment',' But must be broken on every one of these days before they respectively draw to a close.');">¹⁸</span> and the same ruling applies to the Ninth of Ab that falls on a Sabbath eve.<span class="x" onmousemove="('comment',' Ta'an 15b. Cf. previous note.');">¹⁹</span> And it was further taught: After the death of R'Gamaliel,<span class="x" onmousemove="('comment',' Reading of marg. note. Cur. edd. in parenthesis, 'R. Simeon b. Gamaliel'.');">²⁰</span> R'Joshua entered [the academy] to abrogate his ruling,<span class="x" onmousemove="('comment',' Sc. to lay down that the fast may be concluded even on a Sabbath eve in agreement with R. Jose.');">²¹</span>

Teshuvot Maharam