Responsa for Eruvin 81:2

תניא אמר רבי יהודה פעם אחת היינו יושבין לפני ר"ע ותשעה באב שחל להיות בע"ש היה והביאו לו ביצה מגולגלת וגמעה בלא מלח ולא שהיה תאב לה אלא להראות לתלמידים הלכה

R'Judah stated: We were once sitting in the presence of R'Akiba, and the day was a Ninth of Ab that occurred on a Sabbath eve, when a lightly roasted egg was brought to him and he sipped it without any salt. And [this he did] not because he had any appetite for it but in order to show the students what the halachah was.<span class="x" onmousemove="('comment',' That a fast on the Sabbath eve must be broken before the Sabbath begins.');">⁴</span> R'Jose, however, ruled: The fast must be fully concluded.<span class="x" onmousemove="('comment',' Cf. previous note and supra p. 281, n. 10.');">⁵</span> 'Do you not agree with the', said R'Jose to them, 'that when the Ninth of Ab falls on a Sunday one must break off<span class="x" onmousemove="('comment',' His meal on the eve of the Fast.');">⁶</span>

Teshuvot Maharam