Nazir 12A

״צא וקדש לי אשה״ סתם ⁠— אסור בכל הנשים שבעולם. חזקה שליח עושה שליחותו, וכיון דלא פריש ליה, הא לא ידע הי ניהו קדיש ליה.

Go out and betroth a woman for me, without specifying a particular woman; from that moment onward the one who appointed the agent is forbidden to all the women in the world until he finds out which woman the agent betrothed. There is a presumption that an agent performs his assigned agency and that he has betrothed a woman for him, and since the agent did not clarify to him which woman he chose, he therefore does not know which woman is the one betrothed to him. If he now betroths another woman, it is possible that she is the daughter, sister, or mother of the one his agent betrothed on his behalf and is therefore forbidden to him.

איתיביה ריש לקיש לרבי יוחנן: קן סתומה שפרחה גוזל אחד מהן לאויר העולם, או שפרחה לבין חטאות המתות, או שמת אחד מהן ⁠— יקח זוג לשני.

Reish Lakish raised an objection to R' Yoḥanan from a Mishnah (Kinnim 2:1): With regard to an impure person who comes to undergo his purification process, and for this purpose set aside an unspecified nest, meaning a pair of turtledoves or pigeons, to use for his offerings. One is to be a burnt-offering and one is to be a sin-offering, and he had not yet specified which bird will be used for which offering. If one fledgling of the pair flew away and escaped to the open air of the world, or if it flew among birds invalidated for sin-offerings that have been left to die, or if one of them died, in each of these cases the owner of the nest purchases a partner for the second, i.e., remaining, bird. At that point he may decide which is for a sin-offering and which is for a burnt-offering.