Muwatta Malik 389
موطأ مالك#389SahihYahya related to me from Malik from Abu'nNadr, the mawla of Umar ibn Ubaydullah, that Abu Salama ibn Abd ar-Rahman asked him, "Didn't I see your master sit down before praying after he had entered the mosque?" Abu'n-Nadr said, "By that he meant Umar ibn Ubaydullah, and he was finding fault with him for sitting down before praying after he had come into the mosque." Yahya said that Malik said, "It is good to do that but not obligatory
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Salim al-HilaliMaqtu Sahih
In-book reference: 9:64