Musnad Ahmad 935:10

Abdullah narrated to us, Ubaydullah ibn Umar al-Qawariri narrated to me, Ja'far ibn Sulayman narrated to us, Habbab al-Qat'i narrated to us, from Abu Ishaq al-Hamdani, from a man from Abd al-Qays, from his father, who said: The Messenger of Allah (peace and blessings of Allah be upon him) led us in the morning prayer. When he finished his prayer, he turned his face toward us, then said: "Indeed, the heaviest of prayers upon the hypocrites are these two prayers."