Accepting Information Given by a Truthful Person

Bukhari :: Book 9 :: Volume 91 :: Hadith 370

Narrated Salama bin Al-Akwa':

Allah's Apostle said to a man from the tribe of Al-Aslam, "Proclaim among your people (or the people) on the day of 'Ashura' (tenth of Muharram), 'Whosoever has eaten anything should fast for the rest of the day; and whoever has not eaten anything, should complete his fast.' "