Muwatta Malik 344
موطأ مالك#344SahihYahya related to me from Malik from Nafi that Ibn Umar stayed in Makka for ten nights, shortening the prayer, except when he prayed it behind an imam, in which case he followed the imam's prayer
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: 9:19