Reference for Eruvin 163:8
אלמא כיון דמספקא ליה אי נזיר אי לא נזיר הוא לא משעביד נפשיה הכא נמי כיון דלא ידע אי קני אי לא קני לא גמר ומקנה:
For it was taught: R'Judah quoting R'Tarfon stated: 'Neither of them<span class="x" onmousemove="('comment',' Of two men who had a bet, one of them undertaking to be a nazarite if a certain person who passed by was a nazarite and the other undertaking to be a nazirite if that person was not a nazirite.');"><sup>11</sup></span> can possibly be regarded as a nazirite, since naziriteship is valid only when it is definite'.<span class="x" onmousemove="('comment',' Lit., 'distinctly uttered'. V. Sanh. 25a, Naz. 34a. As neither of the two had any knowledge as to whether the man who passed them was, or was not a nazirite, the vow of neither could be definite and neither, therefore, can be deemed valid.');"><sup>12</sup></span>