Yevamot 99A

תנו רבנן: יש חולץ לאמו מספק, לאחותו מספק, לבתו מספק.

§ A baraita states: There is a case in which one performs ḥalitza with his mother due to uncertainty, or with his sister due to uncertainty, or with his daughter due to uncertainty. This is the halakha despite the fact that a levirate bond cannot be created between these relatives.

כיצד? אמו ואשה אחרת, ולהן שני זכרים, וחזרו וילדו שני זכרים במחבא, ובא בנה של זו ונשא אמו של זה, ובנה של זו נשא אמו של זה, ומתו בלא בנים ⁠— זה חולץ לשתיהן, וזה חולץ לשתיהן. נמצא כל אחד ואחד חולץ לאמו מספק.

How so? If his mother and another woman had two sons, one each, and they then gave birth to two other sons in hiding, whose identities were confused, such that their lineage was consequently indeterminate, and the known son of this woman came and married the mother of that other known son, and the known son of that woman married this son’s mother, and they died without children, the halakha is that this one of the mixed sons performs ḥalitza with both women, as it is unknown which is his mother and which his yevama, and that one likewise performs ḥalitza with both women. It is therefore found that each one of them performs ḥalitza with his mother, due to the uncertainty.

לאחותו מספק כיצד? אמו ואשה אחרת שילדו שתי נקבות במחבא, ובאו אחיהן שלא מאותה האם ונשאום, ומתו בלא בנים ⁠— חולץ לשתיהן, נמצא חולץ לאחותו מספק.

There is a case where a man performs ḥalitza with his sister due to uncertainty. How so? If his mother and another woman gave birth to two females in hiding, and they were mixed, and the paternal, but not maternal, half brothers of this man and of the son of the other woman came and married them, and those half brothers died without children, the halakha is that the living half brothers perform ḥalitza with both wives, each with his half sister-in-law. It is therefore found that one performs ḥalitza with his half sister due to uncertainty.