It was narrated that Ibn ‘Abbas said:
“A Bedouin came to the Prophet (ﷺ) and said: ‘I have seen the new crescent tonight.’ He said: ‘Do you bear witness that none has the right to be worshipped but Allah and that Muhammad is the Messenger of Allah (ﷺ)?’ He said: ‘Yes.’ He said: ‘Get up, O Bilal, and announce to the people that they should fast tomorrow.’”