Musnad Ahmad 32:1837

'Abdullah ibn Bakr narrated to us, Humaid narrated to us, from Anas, who said: "We would not wish to see the Messenger of Allah, may Allah bless him and grant him peace, praying except that we saw him, or sleeping except that we saw him." He said: "And he would fast during the month until we would say: 'We do not see him wanting to break any part of it,' and he would break his fast during the month until we would say: 'We do not see him wanting to fast any part of it.'"