Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: A Bedouin came to the Prophet (peace and blessings be upon him) and said: I have seen the moon. The Prophet (peace and blessings be upon him) said: "Do you bear witness that there is no deity except Allah and that I am the Messenger of Allah?" He said: Yes. The Prophet (peace and blessings be upon him) said: "O Bilal! Announce among the people that they should fast tomorrow."