Nedarim 61B

לספיקא, ורבי יוסי סבר: מעייל איניש נפשיה לספיקא.

in a position of uncertainty, and R' Yosei holds that a person does place himself in a position of uncertainty?

ורמינהי: מי שיש לו שתי כיתי בנות משתי נשים, ואמר: קדשתי את בתי הגדולה, ואיני יודע אם גדולה שבגדולות, אם גדולה שבקטנות, ואם קטנה שבגדולות שהיא גדולה מן הגדולה שבקטנות ⁠— כולן אסורות, דברי רבי מאיר. חוץ מן הקטנה שבקטנות.

The Talmud raises a contradiction from the following Mishnah (Kiddushin 64b): In the case of one who has two groups of two daughters born to him from two women, e.g., he has two daughters from his first wife, and after his first wife died he remarried and had two daughters with his second wife, and he said: I betrothed my older daughter to someone, but I do not know if I meant the older of the older group of daughters; or if I meant the older daughter of the younger group; or if I meant the younger daughter of the older group, who is nevertheless older than the older daughter of the younger group, then all 3 of those daughters are prohibited to marry another man due to the uncertainty, as he failed to clarify which daughter was betrothed. This applies to all the daughters apart from the younger daughter of the younger group, who is certainly not betrothed. This is the statement of R' Meir.

רבי יוסי אומר: כולן מותרות, חוץ מן הגדולה שבגדולות.

R' Yosei says: They are all permitted to marry, apart from the older daughter of the older group. This demonstrates that according to R' Meir, one must take into account any of the possible meanings of the imprecise expression: My older daughter, whereas R' Yosei maintains that only the narrowest possible meaning of the phrase is taken into account. This contradicts the Mishnah here.