Musnad Ahmad 31:442

'Abd al-Samad narrated to us, Harb narrated to us, Yahya—meaning Ibn Abi Kathir—narrated to us, he said: Abu Sa'id, the freed slave of al-Mahri, narrated to me, he said: Abu Sa'id al-Khudri narrated to me that the Messenger of Allah, peace and blessings of Allah be upon him, said: "O Allah, bless for us our mudd. O Allah, bless for us our sa', and place with the blessing two blessings."