What is the basis for the majority ruling on the scope of manumission when one partner frees his share?

Primary text

The ruling that the entire slave is freed upon the emancipation of a share by a solvent owner is supported by authentic, agreed-upon Hadith. One narration states that the Prophet (PBUH) established freedom for the whole slave and required the solvent co-owner's portion value to be paid. Another narration indicates that a man who manumitted a portion of a jointly owned slave had its value settled upon him, with the statement, 'Allah has no partner' in this regard. The view of Al-Buti contradicts all reports and should be disregarded. The report concerning Ibn al-Talb must be interpreted as applying to an insolvent emancipator in order to reconcile the narrations. Analogy with sale is invalid because sale does not take effect over the entire slave if only a part is sold, whereas manumission does take effect over the entirety. The Wala' belongs solely to the first emancipator because the freedom was established through his expense.