Muwatta Malik 406
موطأ مالك#406SahihYahya related to me from Malik from Rabia ibn Abi Abd ar-Rahman that if Abdullah ibn Umar arrived at the mosque and the people had already prayed, he would begin with the obligatory prayer and not pray anything before it
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Salim al-HilaliMauquf Sahih Lighairihi
In-book reference: 9:81