What is the basis for requiring the explicit mention of paternity negation during the *Li'an*?

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When a right is waived through *Li'an*, mentioning it becomes a condition, as it is for the wife. Moreover, the ultimate effect of the *Li'an* is establishing adultery, which does not inherently necessitate paternity negation, unlike cases where the wife confesses or witnesses confirm adultery. Regarding the Hadith of Sahl ibn Sa'd, Al-Bukhari narrated that the wife was pregnant and he denied her pregnancy. Ibn Umar narrated that a man performed *Li'an* concerning his wife's offspring during the Prophet's time, and the Prophet separated them and attributed the child to the mother; the addition from a trustworthy narrator is accepted.