Responsa for Nedarim 151:1-152:99:2

אמרי רבנן לא קיימי להון בטעמיה דר"א והכי קאמרי ליה מאי סבירא לך אי סבירא לך דחיילין ובטלין תהוי כלי תיובתך אי לא סבירא לך דחיילין תהוי מקוה תיובתך

— I will tell you: The Rabbis were not clear as to R. Eliezer's standpoint. Hence they said thus to him: What is your opinion? If you maintain that they [the vows] take effect, but are annulled, you are refuted by [the analogy of] a utensil; whilst if you do not hold that they take effect, the mikweh is your refutation. Come and hear: R. Eliezer said to them: If defiled seeds are rendered clean by being sown in the soil, how much more so if [already] sown and rooted [in the soil]!<span class="x" onmousemove="('comment',' That they certainly cannot be defiled. Thus also vows: if a vow can be annulled when already in force, surely the annulment can operate to prevent it from coming into force! ');">³</span>

Teshuvot Maharam