Muwatta Malik 411
موطأ مالك#411SahihYahya related to me from Malik from Ibn Shihab that Said ibn al- Musayyab said, "Which prayer is it when you remain in the sitting position in every raka?'' Said said, "It is maghrib when you miss one raka, and that is the sunna in all the prayers
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: 9:86