Muwatta Malik 1253
موطأ مالك#1253SahihMalik related to me from Nafi that Abdullah ibn Umar said, "The idda of an umm walad when her master dies is one menstrual period
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Salim al-HilaliMauquf Sahih
In-book reference: 29:50