Sayyiduna Ibn Abbas (may Allah be pleased with them both) narrates: A Bedouin came to the Prophet (peace and blessings be upon him) and said: I have seen the new moon tonight. He (peace and blessings be upon him) asked: "Do you testify that there is no true god except Allah and that Muhammad is His servant and His Messenger?" He said: Yes. He (peace and blessings be upon him) said: "O Bilal! Stand up and announce among the people that they should fast." Imam Bukhari used Ikrimah as evidence and Imam Muslim used Simak as evidence, and this hadith with a sahih (authentic) chain is current among the jurists, but the two Shaykhs (Bukhari and Muslim) did not record it.