Musnad Ahmad 33:677

Abu Salamah narrated to us, Bakr bin Mudar informed us, Umarah bin Ghaziyah narrated to me, from Muhammad bin Abd al-Rahman bin As'ad bin Zurarah, from Jabir bin Abdullah, that the Messenger of Allah, peace and blessings of Allah be upon him, during one of his journeys, saw people gathered around a man. The Messenger of Allah, peace and blessings of Allah be upon him, asked [about him], and they said: "A man whom fasting has exhausted." The Messenger of Allah, peace and blessings of Allah be upon him, said: "It is not righteousness to fast while traveling."