Musnad Abu Ya'la al-Mawsili 105:43

Ibn Numayr narrated to us, Abu Khalid al-Ahmar narrated to us, from ‘Amr ibn Qays, from Abu Ishaq, from Silah, who said: We were with ‘Ammar on the day about which there is doubt regarding Ramadan, and a sheep was brought. Some of the people withdrew. ‘Ammar said: "Whoever fasts this day has disobeyed Abu al-Qasim, may Allah bless him and grant him peace."