Responsa for Shabbat 266:3
מאן תנא פירש אינו חוזר אמר רבה בר בר חנה אמר רבי יוחנן רבי ישמעאל בנו של ר' יוחנן בן ברוקה היא דתניא ארבעה עשר שחל להיות בשבת מפשיט (אדם) הפסח עד החזה דברי רבי ישמעאל בנו של ר' יוחנן בן ברוקה וחכ"א מפשיטין את כולו
Who teaches: Once he has withdrawn, he must not return? Said Rabbah b. Bar Hanah in R. Johanan's name: It is R. Ishmael the son of R. Johanan b. Berokah. For it was taught: If the fourteenth [of Nisan] falls on the Sabbath, the passover sacrifice is flayed as far as the breast: this is the view of R. Ishmael the son of R. Johanan b. Berokah. But the Sages maintain: We flay the whole of it.<span class="x" onmousemove="('comment',' v. Supra 116b. When one reaches the breast he temporarily ceases flaying in order to remove the fats; this cessation is analogous to withdrawing in the case of circumcision, and R. Ishmael rules that he must not return to complete the flaying. ');"><sup>4</sup></span> But how so? R. Johanan may rule [thus] only there, because we do not require [the application of the verse,] This is my God, and I will adorn him,<span class="x" onmousemove="('comment',' Ex. XV, 2. Or perhaps, and I will adorn myself for His sake. Once the fats are removed for sacrificial purposes there is no adornment of the precept in trimming the flesh and making it look presentable. ');"><sup>5</sup></span>