"Tell it to us." The old man said: "My paternal uncle told me that he went to the Prophet, concerning some camels of his, while he was eating. He said: 'Come and eat.' I said: 'I am fasting.' He said: 'Allah, the mighty and sublime, has waived half of the prayer and fasting for the traveler, the pregnant woman and the sick."'
Sunan an-Nasa'i Book 22, Hadith 186