Musnad Abu Ya'la al-Mawsili 105:47

Musa ibn Muhammad narrated to us, Muhammad ibn Abi al-Wazir narrated to us, Sufyan ibn 'Uyaynah narrated to us, from 'Umar ibn Habib, from 'Abdullah ibn Kathir, he said: 'Ammar ibn Yasir said: The Messenger of Allah, may Allah bless him and grant him peace, commanded us to lengthen the prayer and shorten the sermon.