Samura b. Jundub reported Allah's Messenger (PBH) as saying:

 The Adhan of Bilal should not mislead you nor the

whiteness  (of the pillar) of dawn, for it is not the

whiteness of the true   dawn, but that of the false dawn

which is vertical like a pillar and you can eat food till the

streaks of whiteness spread like it.                          (Muslim)