Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) narrates: A Bedouin came to the service of the Prophet (peace and blessings be upon him) and said: Last night I saw the new moon of the first (of the month). The Prophet (peace and blessings be upon him) asked: Do you bear witness that there is no deity except Allah and that Muhammad (peace and blessings be upon him) is His servant and His Messenger? He replied: Yes. The Prophet (peace and blessings be upon him) said: O so-and-so, get up and announce among the people that they should fast tomorrow. The same narration is also transmitted with another chain, in which these words are present: "O Bilal, get up."
Hadith Referenceصحیح ابن حبان / كتاب الصوم / 3446
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيضعيف - «ضعيف أبي داود» (402 - 403)، «الإرواء» (907).فضيلة الشيخ العلّامة شُعيب الأرناؤوطNull