Muwatta Malik 306
موطأ مالك#306SahihYahya related to me from Malik from Ismail ibn Muhammad ibn Said ibn Abi Waqqas from a mawla of Amr ibn al-As or of Abdullah ibn Amr ibn al-As that the Messenger of Allah, may Allah bless him and grant him peace, said, "The prayer of one of you sitting down is only equal to half the prayer of one of you when he is standing
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Salim al-HilaliSahih
In-book reference: 8:20