Musnad Ahmad 1304:16

Abu al-Nadr and Hasan ibn Musa narrated to us, they said: Shayban narrated to us, from Layth, from Shahr, from Asma bint Yazid, she said: A drink was brought to the Prophet, may Allah bless him and grant him peace, and it was passed around to the people, and among them was a fasting man. When it reached him, he said to him: "Drink." It was said: "O Messenger of Allah, he is not breaking his fast," or "He is fasting forever." He—meaning the Messenger of Allah, may Allah bless him and grant him peace—said: "He has not fasted, whoever fasts forever."