"When Ramadan starts, an Angel calls out saying...."

Messenger of Allah S.A.W. said during Ramadan:

'The gates of Hell are closed,
the gates of Paradise are opened,
and the devils are in chains.

An angel calls out :
'O you who intend to do good deeds, have glad tidings. O you who intend to do evil, refrain, until Ramadan is completed.''"

(Ahmad and an-Nasa'i)