Nedarim 10A

אפילו תימא רבי יהודה, כי אמר רבי יהודה ⁠— בנדבה, בנדר לא אמר.

Even if you say that the Mishnah is in accordance with the opinion of R' Yehuda, it can be argued that when R' Yehuda said that it is good to take a vow and fulfill it, he said it with regard to a gift offering, but he did not say it with regard to vows.

והקתני: ״טוב מזה ומזה נודר ומקיים״! תני: ״נודב ומקיים״.

The Talmud asks: But isn’t the Mishnah teaching that according to R' Yehuda, better than both this and that is one who vows [noder] and pays, which indicates that he says this even about vows? The Talmud answers: Teach the opinion of R' Yehuda with the following, emended formulation: Better than both this and that is one who volunteers [nodev] a gift offering and pays it.

מאי שנא נודר דלא, דילמא אתי בה לידי תקלה? נדבה נמי, דילמא אתי בה לידי תקלה!

The Talmud asks: What is different about one who vows, i.e., one who says: It is incumbent upon me to bring an offering, which is not proper to do due to the concern that perhaps he will encounter a stumbling block and not bring it promptly, thereby violating the prohibition against delaying? One should also not designate a particular animal as a gift offering, due to the concern that perhaps he will encounter a stumbling block with it.

רבי יהודה לטעמיה, דאמר: אדם מביא כבשתו לעזרה, ומקדישה, וסומך עליה, ושוחטה.

The Talmud answers: R' Yehuda conforms to his standard line of reasoning, as he said explicitly in a baraita: A person brings his lamb to the Temple courtyard and consecrates it there, and immediately leans on it and slaughters it. Consequently, there is no concern that he will encounter a stumbling block.