What is the justification for using casting lots (qur'ah) when determining the divorced wife in cases of ambiguity?

Primary text

The justification rests upon the statement of Ali, which supersedes the opinion of Ibn Abbas, as Ibn Abbas himself deferred to Ali's established position. Furthermore, the release of ownership from a free person (ādamī) permits the use of casting lots during uncertainty, similar to manumission (freedom of a slave), as evidenced by the narration of Imran ibn al-Husayn concerning manumission. Rights being equal where specification is impossible without lots necessitates employing lots, like the division of provisions during travel among wives. Dividing the inheritance equally among all results in giving one wife what she is not entitled to, curtailing the right of others certainly, and suspension leads to the waste of their rights and denies the rightful owner her due.