On the authority of Ibn ʿAbbās, he said: A Bedouin came to the Prophet, peace and blessings be upon him, and said, "I have seen the crescent moon." He said, "Do you bear witness that there is no god but Allah? Do you bear witness that Muhammad is the Messenger of Allah?" He said, "Yes." He said, "O Bilāl, announce to the people that they should fast tomorrow." (1)

700 - Abū Kurayb narrated to us, he said: Ḥusayn al-Juʿfī narrated to us, from Zāʾidah, from Simāk, similar to it. (2)

The ḥadīth of Ibn ʿAbbās contains a discrepancy. Sufyān al-Thawrī and others narrated from Simāk ibn Ḥarb, from ʿIkrimah, from the Prophet, peace and blessings be upon him, as a mursal (incomplete chain), and most of the companions of Simāk narrated from Simāk, from ʿIkrimah, from the Prophet, peace and blessings be upon him, as a mursal. (3)

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(1) Its chain is weak; Simāk, in his narration from ʿIkrimah, had inconsistency, and there was disagreement concerning him in this ḥadīth. It was narrated as mursal and also as connected (mawṣūl), and more than one of the imams favored the mursal version.
It was narrated as connected by Abū Dāwūd (2340), Ibn Mājah (1652), and al-Nasāʾī 4/131-132 and 132. It is in "Ṣaḥīḥ Ibn Ḥibbān" (3446), "Sharḥ Mushkil al-Āthār" by al-Ṭaḥāwī (482-484), and "Sharḥ al-Sunnah" by al-Baghawī (1724).
On this topic, from Ibn ʿUmar, in Abū Dāwūd (2342): The people looked for the crescent moon, and I informed the Messenger of Allah, peace and blessings be upon him, that I had seen it, so he fasted it and ordered the people to fast it. Its chain is sound, and it is in "Ṣaḥīḥ Ibn Ḥibbān" (3447).
(2) Its chain is weak like the previous one; see its takhrīj therein.
(3) The mursal narration was reported by Abū Dāwūd (2341) and al-Nasāʾī 4/132, and it is in "Sharḥ al-Mushkil" (485). Abū Dāwūd said: A group narrated it from Simāk, from ʿIkrimah, as mursal. Al-Zaylaʿī in "Naṣb al-Rāyah" 2/443 quoted al-Nasāʾī's statement: This is more correct.