Musnad Ahmad 30:186

Sufyan narrated to us, from Abu al-Zinad, from al-A'raj, from Abu Hurayrah, attributing it to the Prophet (may Allah bless him and grant him peace): "If one of you is invited to food while he is fasting, let him say: 'I am fasting.'" Abdullah ibn Ahmad said: My father said: "We did not use to call him by the kunya Abu al-Zinad; we used to call him by the kunya Abu Abd al-Rahman."